Hydroponics · Mixing guide
How to Mix Hydroponic Nutrients: Concentrates, Mixing Order, EC and pH
Most reservoir problems start before the plants drink anything: two concentrates poured together, pH adjusted before the last nutrient went in, or a starting EC nobody measured. This guide takes both Greenway hydroponic programs from dry bag to finished reservoir — the five crop formulas used with Calcium Nitrate and magnesium sulfate, and the four-part Cal-Mag Plus, Micro Green, Grow Green, and Blossom Green system. It covers making concentrates, the mixing order, water quality and starting EC, pH, EC by crop and stage, topping off versus changing, and storage. Every amount is taken from the live Greenway product pages, and the label on your bag governs.
See the mixing order Jump to EC and pH targets
- 2 tanks The minimum for concentrates: calcium in one, phosphate and sulfate in the other
- Water first Fill to full volume and read the water’s own EC before any nutrient goes in
- 5.5–6.5 The pH range where most nutrients are highly available in solution
pH last
Every fertilizer you add shifts pH and EC, so adjust pH after the last one
Why Calcium Concentrates Stay Separate from Phosphate and Sulfate
The same fertilizers that work together in a full reservoir turn to sediment when their concentrates meet.
Every recipe in this guide comes back to one piece of chemistry. When nutrient solutions are concentrated, some nutrients form precipitates that can clog drip lines, so Penn State Extension puts calcium in a different stock tank from phosphates and sulfates[1]. Calcium combines with sulfate to form gypsum (calcium sulfate) and with phosphate to form calcium phosphate; both settle to the bottom of the tank, where plant roots cannot use them[2][3]. The most common incompatibility is sulfate with calcium — Epsom salt with calcium nitrate is the classic example — and phosphate can also precipitate with calcium and with iron[11]. The University of Arizona’s hydroponics workshop puts the sulfate half bluntly: when concentrated, calcium must be separated from sulfates to keep gypsum crystals from precipitating[9].
Dilution is what makes them compatible. UMass Extension explains that calcium nitrate and a phosphate fertilizer mixed together as concentrated stock react and settle out, while the same two injected at the same time are diluted as they meet in the water line and can be used together[4]. That is why extension recipes split concentrates into at least two tanks: UF/IFAS keeps calcium nitrate in one and the potash, phosphate, and magnesium sulfate in the other[5][6], and Ohio State separates the calcium portion from the other macronutrients because at 100X concentration it combines with sulfate and phosphate[2]. Missouri Extension puts it plainly: dissolving each fertilizer formulation separately stops the reaction from happening[3].
Which side of the line each Greenway product sits on
Both Greenway programs are built around this rule. The crop formulas carry phosphate (the Lettuce, Cucumber, and Pepper & Herb pages name sulfate too) and no calcium, so calcium comes from Calcium Nitrate or Cal-Mag Plus in a separate container. In the 4-part system, every part is dissolved into its own concentrate and only meets the others in the reservoir.
| Product | What matters for mixing | Keep its concentrate apart from |
|---|---|---|
| Calcium Nitrate 15.5-0-0 | Calcium and nitrate nitrogen | Every phosphate or sulfate concentrate: the crop formulas, Epsom salt, monopotassium phosphate |
| Cal-Mag Plus 2-0-0 | Calcium, magnesium, nitrate nitrogen, and EDTA-chelated iron | Concentrated phosphate or sulfate fertilizers, such as a 4-18-38, monopotassium phosphate, or Epsom salt stock — and the Blossom Green concentrate |
| Micro Green 2-0-3 | Chelated micronutrients, plus a small amount of calcium from its calcium nitrate carrier; no phosphorus | Every other concentrate; its page says never to combine concentrates directly |
| Lettuce 8-15-36, Cucumber 8-16-36, Pepper & Herb 11-11-40 | Phosphate and sulfate; no calcium or magnesium | Calcium Nitrate and Cal-Mag Plus |
| Strawberry 8-12-32, Tomato 4-18-38 | Phosphate; no calcium or magnesium | Calcium Nitrate and Cal-Mag Plus; the tomato page adds: do not mix the dry product with calcium fertilizers |
| Epsom Salt for Plants (magnesium sulfate) | Magnesium and sulfate | Calcium concentrates. UF/IFAS puts magnesium sulfate in the same stock as the potash and phosphate |
| Grow Green 4-2-6 | Nitrogen and potash, with phosphate from monopotassium phosphate and sulfate from potassium and magnesium sulfate | Cal-Mag Plus and Micro Green concentrates |
| Blossom Green 2-6-8 | Phosphate and potash for flowering and fruiting | Cal-Mag Plus concentrate; its page says never to store the two in the same container |
Never pour one concentrate into another
Not into the same jug, not through the same unrinsed funnel, and not into a reservoir that is still nearly empty. Dissolve each product in its own container, add each one to the full volume of water one at a time, and stir between additions. Before trying an unfamiliar combination, run a jar test: dissolve the products at the strengths you plan to use in 1 to 2 quarts of water in a clear jar, cap it, let it stand 12 to 24 hours, and look for cloudiness or solids[11].
Start with Your Water: Test It and Record the Starting EC
Your water is the first ingredient in every batch. Its minerals, alkalinity, and EC change what the fertilizer has to do.
A water test comes before the first bag is opened. UF/IFAS calls testing the well water one of the first steps in a nutrient management program, checking pH, carbonates, sulfur, magnesium, calcium, and iron[5], and its greenhouse handbook says that without an accurate water test a grower cannot claim to have a good fertilizer management program[6]. Missouri Extension asks for pH, EC, alkalinity, and individual elements[3]. Your water utility’s report covers much of this; otherwise have the water tested, as the Cal-Mag Plus page suggests.
What the test tells you
Calcium and magnesium already in the water. They count toward the recipe. UF/IFAS notes that many Florida wells carry 40 to 60 ppm calcium, some but probably not all of it available to the crop[5]. The crop formula pages build this in: their formulas subtract the potassium and calcium already in your water before you weigh anything. Reverse-osmosis and distilled water bring little or no calcium or magnesium, so the nutrients must supply all of it.
Alkalinity. Alkalinity, mostly carbonates and bicarbonates, sets how much acid it takes to move the pH of your water. Oklahoma State notes that water with alkalinity above 75 ppm will raise the pH of nutrient solutions[7], and Missouri Extension notes that above about 160 ppm it takes higher amounts of acid to change the pH[3]. High-alkalinity water is the usual reason a reservoir’s pH creeps upward faster than expected.
Sodium and chloride. Missouri Extension lists less than 50 ppm sodium and less than 70 ppm chlorine as the optimum range for hydroponic source water, and an EC ideally below 1 dS/m[3]. Fertilizer cannot remove them, and Ohio State cautions that too-saline source water must be avoided or used only after appropriate consultation[2].
Record the starting EC
Fill a clean container with the water you will mix with and read its EC before adding anything. Cornell’s lettuce handbook tells growers to subtract the base EC of the source water from the meter reading, and it runs its lettuce ponds at about 1,200 µS/cm (1.2 mS/cm) above the source water[8]. The Greenway 4-part schedule does not say whether its EC targets include the water’s own EC. If your plain water reads close to zero, the question does not arise; if it reads high, email us your water test before relying on the schedule’s EC column.
EC is a measure of the total salts in a solution[7]. It does not confirm that each nutrient is at its target concentration[3], and it cannot tell you whether your water’s salts are calcium, magnesium, or sodium. Use it to check strength; use the water test to decide how much calcium and magnesium to add.
What you need on the bench
- A digital scale for the crop formulas and Calcium Nitrate. The product pages give weights because the weight of a spoonful has not been measured; the lettuce page notes that a kitchen scale reading to 0.1 g is enough.
- A syringe, graduated cylinder, or measuring cup marked in milliliters for the 4-part concentrates, as the Cal-Mag Plus page directs.
- An EC meter and a pH meter, calibrated. Oklahoma State calibrates the EC meter in a standard solution of known EC, usually 1.41 mS/cm[7], and Cornell recommends calibrating all sensors on a regular basis[8].
- Separate, clean, opaque containers with lids — one per concentrate — and a label and marker for each.
- Nitrile gloves and safety glasses with side shields, and chemical splash goggles when mixing concentrated solutions, as the product pages and Safety Data Sheets direct.
Units, briefly: mS/cm and dS/m are the same number, and µS/cm divided by 1,000 gives mS/cm. Greenway’s schedules and the university sources here give EC, not ppm, so if your meter can display EC, use that setting to compare readings directly with the tables. The ppm in a recipe — 200 ppm potassium, 150 ppm calcium — are milligrams of one nutrient per liter of solution, not a meter reading.
How to Make Concentrates (Stock Solutions) from the Dry Bags
The 4-part system turns each bag into a liquid you measure by the milliliter. The crop formulas are weighed, into a fresh batch or into an injector stock.
A stock solution is a concentrate you dilute into the reservoir. Penn State notes that solutions can be supplied at normal strength or concentrated, commonly at 50, 100, or 200 times normal strength depending on the injector and the solubility of the fertilizers[1]. The two Greenway systems use concentrates differently, so mix each one the way its pages describe.
The 4-part system: one bag, one batch of concentrate
Each 4-part product is a dry powder that you dissolve into a set volume of water. You then dose that concentrate by the milliliter per gallon of reservoir water.
| Product | Mix | Bag size → concentrate | Mixing water, per the page | Page notes |
|---|---|---|---|---|
| Cal-Mag Plus 2-0-0 | 2.5 lb per gallon of water (the label prints 25 lb in 10 gallons) | 2.5, 5, 10, 25 lb → about 1, 2, 4, 10 gallons | Warm, not boiling (Safety Data Sheet) | Dissolve the entire bag; the label says not to divide it |
| Grow Green 4-2-6 | 1.7 lb per gallon of water | 1.7, 3.4, 8.5, 17 lb → 1, 2, 5, 10 gallons | Warm, 65–75°F | Mixing the entire package at once keeps the concentration uniform; shake before each use |
| Micro Green 2-0-3 | 1.5 lb per gallon of water | 1.5, 3, 7.5, 15 lb → 1, 2, 5, 10 gallons | Clean, room-temperature water; RO or low-EC preferred | Let stand 30 minutes; store in a dark, opaque container |
| Blossom Green 2-6-8 | 1.8 lb per gallon of water | 1.8, 9, 18, 36 lb → 1, 5, 10, 20 gallons | Warm, 70–80°F; let the stock cool to room temperature before dosing | Never store in the same container as Cal-Mag Plus concentrate |
- Label four clean containers, one per product, with the product name and the date. Opaque containers with tight lids keep light off the chelated iron and micronutrients.
- Measure the water for the bag size from the table, at the temperature its page gives.
- Add the powder slowly and stir until it is fully dissolved. Warm water, aeration, and constant mixing help salts dissolve[9]. The Cal-Mag Plus page notes that the dissolved powder adds a little volume, so a bag makes slightly more concentrate than the water you started with.
- Seal and store each container in a cool, dark place, out of reach of children and pets.
- Never combine the concentrates. They meet only in the reservoir.
Cloudy concentrate?
The Cal-Mag Plus Safety Data Sheet says to discard its concentrate if it turns cloudy or forms a precipitate. The Grow Green page notes that cloudy stock typically means hard water and suggests RO or distilled water for stock preparation when possible. Some settling in a saturated Grow Green stock is normal, which is why its page says to shake before each use.
The crop formulas and Calcium Nitrate: weigh to a target
The crop formula labels give no hydroponic “bag into so many gallons” recipe. Instead, each product page doses the formula to the potassium target of a published university recipe, and doses Calcium Nitrate to a calcium target. Magnesium comes from magnesium sulfate, weighed by your recipe or water test.
The formulas on the product pages
- Crop formula: grams of product = (potassium target in ppm − potassium already in your water in ppm) × liters of final solution ÷ the product’s divisor: 299 for Lettuce 8-15-36 and Cucumber 8-16-36, 265.6 for Strawberry 8-12-32, 332 for Pepper & Herb 11-11-40, and 315.4 for Tomato 4-18-38.
- Calcium Nitrate 15.5-0-0: grams of product = (calcium target in ppm − calcium already in your water in ppm) × liters of final solution ÷ 190. Each gram per liter also adds 155 ppm nitrogen, so count that nitrogen in your recipe.
- Volume: multiply US gallons by 3.785 to get liters.
Fresh batch (most home systems). Weigh each product for the volume you are mixing, dissolve each one on its own in a bucket of water, and add each to the full reservoir following the mixing order below. The calculators on each product page do the arithmetic.
Injector stocks (larger systems). Two stock tanks feed two injectors at 1:100, which means 1 gallon of each stock per 100 gallons of final solution. One tank holds the crop formula, plus magnesium sulfate where your recipe calls for it; the other holds Calcium Nitrate. UMass Extension runs its two greenhouse tomato stocks at the same time, each at 1:100, so they mix only after dilution[4]. The product pages give these stock strengths:
| Formula | Potassium target | Stock strength on the page |
|---|---|---|
| Lettuce 8-15-36 | 200 ppm (University of Arizona CEAC leafy-green recipe) | About 67 g per liter. Worked example: a 30-gallon stock from water with 5 ppm potassium is 16.34 lb (7,410 g) in the tank, 247 g per gallon of stock |
| Cucumber 8-16-36 | 150 ppm (UF/IFAS cucumber formula) | A 30-gallon stock from water with 5 ppm potassium is 12.15 lb (5,510 g) in the tank, 184 g per gallon of stock |
| Strawberry 8-12-32 | 117 ppm (Yamazaki strawberry solution) | About 44 g per liter from potassium-free water. A 30-gallon stock from water with 5 ppm potassium is 10.56 lb (4,788 g) in the tank, 160 g per gallon of stock |
| Pepper & Herb 11-11-40 | 200 ppm after first flower (UF/IFAS pepper solution) | About 60 g per liter from potassium-free water, or 110 g per liter with magnesium sulfate for 50 ppm magnesium |
| Tomato 4-18-38 | About 200 ppm (UF/IFAS 4-18-38 recipe) | 16 lb of 4-18-38 and 10 to 12 lb of magnesium sulfate in one 30-gallon stock tank; Calcium Nitrate in a separate 30-gallon tank at 7.5 to 20.5 lb, rising by growth stage; both injected at 1:100 |
Check every new stock before you rely on it. The crop formula pages say to dissolve the product in warm water and check that nothing settles out; if it does, use a lower injector ratio, which makes a weaker stock (for example, 1:100 instead of 1:200). For the Calcium Nitrate tank, the only stock weights on the pages are for tomatoes. With Tomato 4-18-38, use the calcium stock weights from the Tomato 4-18-38 page in the table above; the Calcium Nitrate page’s tomato weights belong to a different UF/IFAS formula. For other crops, size the calcium stock from the calcium formula above, or email us your recipe and injector ratio.
How to Mix a Hydroponic Reservoir, Step by Step
Water, calcium, micronutrients, the phosphate and sulfate side, EC, and pH last. Stir between every step.
- Fill the reservoir with the full volume of water. Measure and write down the water’s EC, pH, and temperature before adding anything. A full reservoir means each concentrate is diluted the moment it goes in.
- Add the calcium source first, and stir. In the 4-part system that is Cal-Mag Plus concentrate at the schedule rate. With a crop formula it is Calcium Nitrate, weighed and dissolved on its own in a separate container, then poured in.
- Add the micronutrients, and stir. In the 4-part system, Micro Green goes in second, after the Cal-Mag Plus has mixed through. The crop formulas already carry EDTA-chelated iron, manganese, zinc, and copper plus boron and molybdenum, and their pages say not to add a micronutrient mix on top.
- Add the phosphate and sulfate side, one product at a time, stirring between them. In the 4-part system that is Grow Green during the vegetative and transition stages and Blossom Green from the transition on. With a crop formula, it is the formula and then magnesium sulfate, each dissolved separately first.
- Circulate, then measure EC. Compare the reading with the target for your crop and stage, allowing for your water’s starting EC. If it is high, add plain water to bring it down[7][8]. If it is far off in either direction, recheck your weights and milliliters before adding anything else.
- Adjust pH last. The pH and EC of a nutrient solution change as each fertilizer dissolves[3], so a pH set before the last product went in will not hold. Add pH up or pH down in small doses, stir, wait, and measure again.
- Look, then log. The finished solution should be clear, with no cloudiness or sediment. Write down the final EC, pH, volume, and what went in. Those notes are what make the next batch faster to diagnose.
Why calcium goes in first. Greenway’s 4-part pages add Cal-Mag Plus to the full reservoir before any phosphate-containing nutrient, so its calcium is already at working strength when Grow Green and Blossom Green arrive. The Micro Green page adds that the calcium and magnesium should be fully dissolved and diluted before the chelated micronutrients go in. The crop formula pages set no order beyond dissolving each product separately and diluting each into the final solution, then checking for cloudiness, EC, and pH; following the same calcium-first routine for both systems keeps one habit at the bench.
A worked dose from the Cal-Mag Plus page
A 20-gallon reservoir at the Cal-Mag Plus starting rate of 5 mL per gallon takes 100 mL of concentrate per fill. For any 4-part product, multiply the schedule’s milliliters per gallon by the gallons of water in the batch.
Mixing the Crop Formulas with Calcium Nitrate and Magnesium Sulfate
Each crop formula is one side of a three-part program: the formula for potash, phosphate, and micronutrients; Calcium Nitrate for calcium and most of the nitrogen; magnesium sulfate for magnesium.
The five Greenway crop formulas — Lettuce 8-15-36, Cucumber 8-16-36, Strawberry 8-12-32, Pepper & Herb 11-11-40, and Tomato 4-18-38 — are water-soluble, potash-rich formulas with EDTA-chelated micronutrients. None contains calcium or magnesium, and at its recipe dose each supplies less nitrogen than the recipe calls for. In solution, each product page doses the formula to the potassium target of a university recipe, then fills the calcium, nitrogen, and magnesium gaps from Calcium Nitrate 15.5-0-0 and Epsom Salt for Plants (magnesium sulfate).
| Formula and recipe | Crop formula | Calcium Nitrate | Magnesium sulfate |
|---|---|---|---|
| Lettuce 8-15-36 — University of Arizona CEAC leafy-green recipe, 200 ppm potassium | 0.67 g per liter | 0.84 g per liter for 160 ppm calcium from water with none; 0.68 g per liter from water that already has 30 ppm | 0.5 g per liter for 50 ppm magnesium (the UF/IFAS figure the page cites) |
| Cucumber 8-16-36 — UF/IFAS cucumber formula, 150 ppm potassium | 0.50 g per liter | 0.68 g per liter for 130 ppm calcium (seeding to first fruit); 1.37 g per liter for 260 ppm (first fruit on), from water with none | 0.5 g per liter for 50 ppm magnesium |
| Strawberry 8-12-32 — Yamazaki strawberry solution, 117 ppm potassium | 0.44 g per liter | 0.21 g per liter for 40 ppm calcium from water with none | 0.12 g per liter adds about 12 ppm magnesium |
| Pepper & Herb 11-11-40 — UF/IFAS pepper solution, 120 ppm potassium to first flower, 200 ppm after | 0.36 g per liter (1.37 g per US gallon), then 0.60 g per liter (2.28 g per US gallon) | 0.63 g per liter for 150 ppm calcium from water with 30 ppm; 0.79 g per liter from water with none | 0.5 g per liter adds about 50 ppm magnesium |
| Tomato 4-18-38 — UF/IFAS 4-18-38 recipe, about 200 ppm potassium | 0.64 g per liter (2.42 g per US gallon at every stage) | Per US gallon, by stage: 1.13 g, 1.44 g, 1.81 g, 2.49 g, 3.10 g | Per US gallon, by stage: 1.51 g for stages 1–3, 1.81 g for stages 4–5 |
The tomato stages run from transplant to first cluster (1), first to second cluster (2), second to third cluster (3), third to fifth cluster (4), and fifth cluster to the end of the crop (5). For tomatoes the page notes that UF/IFAS targets less potassium early in the crop — 120 ppm in stages 1 and 2 and 150 in stages 3 and 4 — and gives the divisor of 315.4 for dosing to those lower targets.
Worked examples from the product pages
- Lettuce, 50 gallons at 200 ppm potassium from water with no potassium: 126.7 g of Lettuce 8-15-36, plus 129.5 g of Calcium Nitrate in a separate container for 160 ppm calcium from water with 30 ppm.
- Cucumber, 50 gallons at 150 ppm potassium from water with no potassium: 95.0 g of Cucumber 8-16-36, plus 99.6 g of Calcium Nitrate for 130 ppm calcium from water with 30 ppm.
- Strawberry, 50 gallons at 117 ppm potassium from water with no potassium: 83.4 g of Strawberry 8-12-32, plus 39.8 g of Calcium Nitrate for 40 ppm calcium from calcium-free water.
- Calcium only, 50 gallons raised from 30 to 150 ppm calcium: 119.5 g of Calcium Nitrate, which adds 97.9 ppm nitrogen.
Three cautions the crop formula pages repeat
Calcium Nitrate brings nitrogen with it. Every gram per liter adds 190 ppm calcium and 155 ppm nitrogen, so the two always rise together. The more calcium your water already holds, the less Calcium Nitrate you add and the further nitrogen falls short of the recipe. If that happens, the pages ask you to email us, because the recipe then needs another nitrate source without calcium or potassium.
Do not stack a micronutrient mix on top. At these doses the formulas already supply more of some micronutrients than the recipes call for — the lettuce page puts zinc and copper at about 7 times the CEAC recipe. Add any micronutrient only if a water or plant tissue test calls for it.
More potassium is not better. UF/IFAS cautions that high potassium can interfere with the plant’s ability to absorb calcium and magnesium[5]. Dose to your recipe’s potassium target, not above it, and supply the calcium.
Using Cal-Mag Plus as the calcium source instead. The crop formulas also pair with Cal-Mag Plus, sold together as the Specialty Fertilizer and Cal Mag Plus bundle. Cal-Mag Plus is dosed by volume, 5–10 mL per gallon, and its label does not state how many ppm of calcium or magnesium each milliliter adds. If your recipe is written in ppm, weighed Calcium Nitrate and magnesium sulfate hit the target; that combination comes as the crop formula, Calcium Nitrate, and Epsom salt bundle.
Mixing the Greenway 4-Part System by Growth Stage
Four concentrates, each with one job, dosed in milliliters per gallon and shifted as the crop moves from vegetative growth to bloom.
The Complete 4-Part Hydroponic Nutrient System splits a nutrient program into four parts so each can be adjusted on its own: Cal-Mag Plus 2-0-0 for calcium, magnesium, and chelated iron; Micro Green 2-0-3 for trace elements; Grow Green 4-2-6 for nitrogen and potash during vegetative growth; and Blossom Green 2-6-8 for phosphate and potash in bloom. Cal-Mag Plus and Micro Green run at every stage; Grow Green tapers off as Blossom Green takes over.
| Growth stage | Cal-Mag Plus | Micro Green | Grow Green | Blossom Green | EC target | pH |
|---|---|---|---|---|---|---|
| Seedlings / clones, weeks 1–2 | Follow the label* | 1.25 | 1.25 | 1.25 | 0.5–0.8 | 5.5–6.5 |
| Early vegetative, weeks 3–4 | 5 | 5 | 5 | 5 | 1.0–1.4 | 5.5–6.5 |
| Late vegetative, weeks 5–6 | 7.5 | 10 | 15 | 5 | 1.4–1.8 | 5.5–6.5 |
| Transition, weeks 7–8 | 10 | 10 | 10 | 10 | 1.6–2.0 | 5.5–6.5 |
| Early bloom, weeks 9–10 | 10 | 10 | 5 | 15 | 1.8–2.2 | 5.5–6.5 |
| Peak bloom, weeks 11–13 | 10 | 10 | 0 | 20 | 2.0–2.5 | 5.8–6.5 |
| Late bloom / flush, week 14+ | 5 | 7.5 | 0 | 15 | 1.5–2.0 | 5.8–6.5 |
*The feeding schedule lists 2.5 mL of Cal-Mag Plus per gallon for seedlings and clones, below the Cal-Mag Plus label rate of 5–10 mL per gallon. Follow the label. The Cal-Mag Plus page says to start at 5 mL per gallon and go higher within the range only when a solution test or your nutrient program calls for more calcium and magnesium.
How to use the schedule
Mix in order. Cal-Mag Plus first, then Micro Green, then Grow Green (vegetative and transition stages), then Blossom Green, each into a reservoir already filled with water, and adjust pH last.
Treat the weeks as a guide. The Blossom Green page says timing varies by crop, light intensity, and environment, and to use EC readings as your primary guide rather than calendar weeks alone. Leafy greens and herbs are harvested before they flower; the Grow Green page gives lettuce, kale, chard, basil, and similar leafy crops a typical vegetative-stage dose of 5–10 mL per gallon.
Make the bloom switch gradually. The Grow Green page runs a 1–2 week transition with Grow Green and Blossom Green at similar rates, around 10 mL per gallon each, then tapers Grow Green down as Blossom Green takes over.
Start low if you are new to the system. The 4-part bundle page suggests starting at the early vegetative rates even if your plants are larger, and increasing rates by 25% per reservoir change until you reach the target EC range for the stage.
Keep the products together. The Micro Green page says to use it only with the Greenway 4-part system, because concentrated calcium fertilizers from other brands can cause precipitation. Jar-test any other combination before it goes into the main reservoir.
Target EC and pH by Crop and Growth Stage
EC tells you how strong the solution is. pH decides how much of it the roots can take up.
The figures below are the ones quoted on Greenway’s product pages, with the university source each page names. University sources differ, so use a range as a starting point, start at the low end, measure your own solution, and watch the plants.
| Crop | EC | pH |
|---|---|---|
| Lettuce and leafy greens | 1.2 to 1.8 mS/cm (Oklahoma State); about 1.2 mS/cm above the source water (Cornell) | 5.8 optimum, 5.6 to 6.0 acceptable (Cornell); the CEAC recipe sets 5.6 |
| Cucumbers | 1.7 to 2.0 mS/cm (Oklahoma State) | 5.5 to 6.0 (UF/IFAS) |
| Strawberries | 1.0 dS/m or less (University of Arizona CEAC); 1.8 to 2.2 mS/cm (Oklahoma State) | 5.5 to 6.0 (University of Arizona CEAC); 6.0 (Oklahoma State) |
| Peppers | 0.8 to 1.8 mS/cm (Oklahoma State) | 5.8 to 6.2 (UF/IFAS); 5.5 to 6.0 (Oklahoma State) |
| Basil | 1.0 to 1.6 (Oklahoma State) | 5.5 to 6.0 (Oklahoma State) |
| Tomatoes | About 2.0 dS/m early in the crop, rising toward 2.4 later (Ohio State); 2.0 to 4.0 mS/cm (Oklahoma State) | 5.8 to 6.2 (UF/IFAS); 6.0 to 6.5 (Oklahoma State) |
| Greenway 4-part system | 0.5–0.8 for seedlings and clones, rising to 2.0–2.5 at peak bloom (schedule above) | 5.5–6.5; 5.8–6.5 at peak and late bloom |
Strawberries are the crop where the sources disagree most. The strawberry page notes that FAO lists a soil salinity threshold of 1.0 dS/m for strawberry and that the University of Arizona notes growers often flush when root-zone EC exceeds 1.2, while Oklahoma State’s table runs higher. Start at the low end with berries.
Why pH 5.5 to 6.5
Ohio State gives 5.5 to 6.5 as the range where most nutrients are highly available[2], Missouri Extension gives the same range as the optimum for most hydroponic crops[3], and UF/IFAS notes that most elements are absorbed best between 5.5 and 6.5 and that holding the solution at 5.6 to 6.0 favors phosphorus uptake[6]. Above that range, iron and manganese become less soluble[12], and the University of Arizona workshop notes that phosphorus, manganese, and boron lockout can occur when pH is too high, around 7.5[9]. Chelates help only so far: UF/IFAS reports that at pH 7.5 only about 2.5% of EDTA-chelated iron is still chelated[14], and the University of Arizona notes that when root-zone pH exceeds 7.0, young strawberry leaves turn yellow-green, a sign of iron deficiency[10].
How to adjust pH
Adjust after every nutrient is in and the solution has circulated. Use a generic pH up or pH down in small doses, stir, wait a few minutes, and measure again; it is easier to add a second small dose than to undo an overshoot. Missouri Extension recommends potassium bicarbonate or potassium hydroxide to raise pH and advises against sodium-based products, because sodium can be toxic to plants; to lower pH, mineral or organic acids are used, and the amount needed depends on your water’s alkalinity[3]. Cornell’s lettuce system adjusts to 5.8 with potassium hydroxide or nitric acid[8]. Add pH adjusters to the diluted reservoir, never to a nutrient concentrate.
Why pH drifts upward
Plant roots change the solution as they feed. When roots take up nitrate, they release hydroxide or bicarbonate, which makes the root zone more basic; ammonium uptake does the opposite[12]. Cal-Mag Plus supplies all of its nitrogen as nitrate and Calcium Nitrate 14.5 of its 15.5%, and nitrate is most of the nitrogen in the Lettuce, Cucumber, Strawberry, and Pepper & Herb formulas, so a slow rise in pH between fills is expected. Oklahoma State advises checking pH and EC daily, at the same time of day[7].
Topping Off vs. Changing the Reservoir
Top off with water as the plants drink. Replace the whole solution on a schedule, because what is left drifts away from the recipe.
A reservoir does not stay the recipe you mixed. Plants absorb different amounts of each nutrient, so the concentration of each one in the solution changes over time[6], and they draw water at their own rate too. EC tells you the overall strength; it does not tell you which nutrients have run down[3].
When to top off with plain water
Oklahoma State notes that water may need to be added daily to replace what the plants use[7]. When the level falls and EC rises, the plants are taking more water than nutrients; Cornell lowers a rising EC by adding pure water[8]. The 4-part bundle page says to top off with plain, pH-adjusted water between reservoir changes, and the Blossom Green page says that if EC climbs above target, to top off with plain pH-adjusted water rather than adding more nutrient solution.
When EC falls between changes
Cornell raises a falling EC with a small quantity of concentrated nutrient stock[8], and Oklahoma State adds nutrient concentrate until the optimum is reached[7]. For Greenway’s crop formulas, the product pages say that in a recirculating system you should replace the solution on schedule rather than topping it up with more of the formula; the same pages note that the formulas already supply more of some micronutrients than the recipes call for. The 4-part pages give no top-up dose. If EC falls well below the stage target mid-cycle, email us before adding concentrate.
How often to change the whole reservoir
| Program or system | Change interval | Where it comes from |
|---|---|---|
| Greenway 4-part system | Full reservoir change every 7–14 days | 4-part bundle page |
| 4-part system in DWC or RDWC | Weekly | Grow Green and Micro Green pages |
| Crop formula solutions | Replace completely every two weeks, checking pH and EC daily | Oklahoma State, as cited on the lettuce, strawberry, pepper, and tomato pages[7] |
| Cucumber solutions | Every one to two weeks | Cucumber 8-16-36 page |
| Recirculating greenhouse systems | Flush the sump tank once a week and mix new solution | UF/IFAS[6] |
Reservoir temperature and oxygen
Warmer water holds less dissolved oxygen, which is why some growers chill their reservoirs[3]. Oklahoma State calls a water temperature of 72 to 75°F optimal[7]; Cornell keeps its lettuce ponds no warmer than 25°C (77°F) and finds that lettuce grows satisfactorily at a dissolved oxygen level of at least 4 ppm[8]. Keep the reservoir aerated, and check the roots whenever you change the solution. Roots that turn brown or slimy point to a different problem from mixing; see our guide to root rot in hydroponics.
Storing Dry Bags and Mixed Concentrates
Dry, sealed, and cool for the bags. Sealed, labeled, opaque, and within its storage window for every concentrate.
| Product | Dry bag | Mixed concentrate |
|---|---|---|
| Cal-Mag Plus 2-0-0 | Store at 55–75 °F, protected from heat, light, and moisture, as the label directs; do not use if the seal is broken | Sealed, labeled, opaque container; up to 2–4 weeks (Safety Data Sheet); discard if cloudy or if a precipitate forms |
| Grow Green 4-2-6 | Sealed in its original container, cool and dry, away from direct sunlight | Opaque, sealed container, cool and dark; the page gives 6+ months; shake before each use |
| Micro Green 2-0-3 | Sealed in its original container, cool and dry, away from direct sunlight | Dark, opaque container; the page gives 6+ months out of light |
| Blossom Green 2-6-8 | Cool, dry place in the sealed bag or an airtight container; it absorbs moisture, so reseal between uses | Sealed, labeled container out of direct light; the page gives 6+ months; never in the same container as Cal-Mag Plus |
| Crop formulas | Original container, sealed, in a cool, dry, well-ventilated place — 40 to 95°F on the Lettuce, Cucumber, Strawberry, and Tomato pages, 50 to 85°F on the Pepper & Herb page. The Lettuce, Cucumber, Strawberry, and Pepper & Herb pages note that they contain potassium nitrate; keep all five away from heat, flames, and combustible materials | The pages give no storage time for a mixed stock; follow the label |
| Calcium Nitrate 15.5-0-0 | Original container, tightly closed, cool, dry, well-ventilated, out of direct sunlight, locked up; reseal after each use; away from organic and combustible materials | The page gives no storage time for a mixed stock; follow the label |
| Epsom Salt for Plants | Sealed, cool, and dry; it keeps indefinitely when stored properly | Keep any magnesium sulfate stock out of the calcium tank |
Light is the reason for opaque containers. Iron chelates such as Fe-EDTA break down in fertilizer solutions exposed to light[13], and the Cal-Mag Plus and Micro Green pages both call for dark, opaque storage for that reason. The 4-part bundle page adds two limits for the whole set: keep products away from heat sources above 90°F, and do not store prepared concentrates for more than 6 months.
Mix only what you will use. Because the Cal-Mag Plus label requires dissolving the whole bag and its concentrate keeps 2–4 weeks, the Cal-Mag Plus page notes that even the 2.5 lb bag makes more concentrate than most home reservoirs use in that time, and suggests choosing the smallest bag that covers the batches you will mix in those weeks.
Safety: for plants only
These products and their concentrates are for feeding plants only — not for human or animal consumption. Keep dry products, concentrates, and mixed reservoirs out of reach of children and pets. Wear nitrile gloves and safety glasses with side shields when handling powder, and chemical splash goggles when mixing concentrated solutions, as the product pages and Safety Data Sheets direct; avoid raising or breathing dust. Calcium Nitrate carries a Danger warning: it is harmful if swallowed and causes serious eye damage. If any product gets in the eyes, flush with clean running water for at least 15 minutes and get medical attention as the product page directs. Label every container with the product and the date, and keep concentrates away from food, feed, and drinking water. Poison Control: 1-800-222-1222.
Fixing Common Mixing Problems
Most reservoir trouble traces back to the order, the water, or the meter. Check those before changing the recipe.
| What you see | Likely cause | What to do first |
|---|---|---|
| The reservoir turns milky, or white sediment settles, right after mixing | Calcium met phosphate or sulfate before dilution — concentrates poured together, or added to a nearly empty reservoir | Mix a fresh batch: full volume of water first, one product at a time, stirring between them; jar-test the combination |
| Cal-Mag Plus concentrate is cloudy or has a precipitate | Past its storage window, or a reaction in the container | Discard it, as its Safety Data Sheet directs, and mix a new bag in a clean container |
| EC far above target right after mixing | A weighing or measuring error, the water’s own EC not counted, or the wrong stage’s rates | Add plain water to bring it down; recheck your weights and the stage |
| Water level falling and EC rising between changes | The plants are taking up more water than nutrients | Top off with plain water |
| pH climbs a little every day | Nitrate uptake by the roots; high-alkalinity source water | Adjust in small steps once a day; test your water’s alkalinity |
| New leaves yellow between green veins | pH has drifted too high for iron uptake | Check and correct pH first; use the deficiency identifier before adding any single nutrient |
| EC drops fast mid-cycle | Plants using nutrients faster than the change interval assumes | Change the reservoir on schedule; with a crop formula, do not top up with more formula |
Key takeaways
- Never let calcium concentrates (Calcium Nitrate, Cal-Mag Plus) meet phosphate or sulfate concentrates (the crop formulas, Epsom salt, Grow Green, Blossom Green). Dilute each into the full reservoir separately.
- Test the water first and record its starting EC. Alkalinity drives pH drift; calcium and magnesium in the water count toward the recipe.
- 4-part concentrates: one bag per gallon at 2.5 lb (Cal-Mag Plus), 1.7 lb (Grow Green), 1.5 lb (Micro Green), and 1.8 lb (Blossom Green). Mix Cal-Mag Plus, Micro Green, Grow Green, Blossom Green, then pH.
- Crop formulas are weighed to a potassium target, with Calcium Nitrate and magnesium sulfate dissolved separately. Do not add a micronutrient mix on top.
- Adjust pH last, aim for 5.5 to 6.5 or your crop’s narrower range, and expect it to rise as plants take up nitrate.
- Top off with plain water; replace the whole solution on schedule. Store concentrates sealed, labeled, and out of light, and Cal-Mag Plus concentrate for no more than 2–4 weeks.
Two hydroponic programs, one mixing rule.
4-part
Complete 4-Part Hydroponic Nutrient System
Cal-Mag Plus, Micro Green, Grow Green, and Blossom Green together, each dissolved into its own concentrate and dosed by stage.
Ca + Mg + Fe
Cal-Mag Plus 2-0-0
Calcium, magnesium, and EDTA-chelated iron. The first concentrate into the reservoir, at 5–10 mL per gallon.
Calcium side
Calcium Nitrate 15.5-0-0
Weighed calcium and nitrate nitrogen for crop formula programs: 190 ppm calcium and 155 ppm nitrogen per gram per liter.
Mg + S
Epsom Salt for Plants
Magnesium sulfate for the magnesium in a crop formula program. Dissolve it separately, and keep it out of the calcium tank.
Crop formulas: Lettuce 8-15-36 · Cucumber 8-16-36 · Strawberry 8-12-32 · Pepper & Herb 11-11-40 · Tomato 4-18-38. Bundles: crop formula with Calcium Nitrate and Epsom salt · crop formula with Cal-Mag Plus. The 4-part parts on their own: Grow Green 4-2-6 · Micro Green 2-0-3 · Blossom Green 2-6-8. Shop by category: hydroponic nutrients · specialty fertilizers.
Mixing hydroponic nutrients: common questions
What order do you mix hydroponic nutrients in?
Fill the reservoir with the full volume of water and measure its EC and pH first. Add the calcium source next: Cal-Mag Plus in the Greenway 4-part system, or Calcium Nitrate dissolved on its own when you use a crop formula. Stir, then add each remaining product one at a time, stirring between them: Micro Green, then Grow Green or Blossom Green, or the crop formula and magnesium sulfate. Measure EC, then adjust pH last.
Can I mix calcium nitrate and Epsom salt together?
Not as concentrates. Concentrated calcium reacts with sulfate to form gypsum and with phosphate to form calcium phosphate, and both settle out as solids that plants cannot use and that can clog lines and emitters. Dissolve each product in its own container or stock tank and let them meet only in the full volume of reservoir water, where they can be used together. Jar-test any combination you have not used before.
How do I make stock solutions from the 4-part bags?
Dissolve each bag in its own labeled container: Cal-Mag Plus at 2.5 lb per gallon of water, Grow Green at 1.7 lb per gallon, Micro Green at 1.5 lb per gallon, and Blossom Green at 1.8 lb per gallon. Dissolve the whole bag; the Cal-Mag Plus label says not to divide it. Stir until fully dissolved, date the container, and store it sealed and out of light. Then dose each concentrate in milliliters per gallon of reservoir water from the feeding schedule.
How much crop formula do I add per gallon?
The crop formula pages dose to a potassium target instead of a fixed spoon rate: grams = (target ppm potassium minus the potassium in your water) x liters of final solution, divided by 299 for Lettuce 8-15-36 and Cucumber 8-16-36, 265.6 for Strawberry 8-12-32, 332 for Pepper and Herb 11-11-40, or 315.4 for Tomato 4-18-38. The UF/IFAS tomato recipe, for example, uses 2.42 g of Tomato 4-18-38 per gallon. Weigh Calcium Nitrate and magnesium sulfate separately.
What pH should a hydroponic reservoir be?
Most hydroponic crops are grown between pH 5.5 and 6.5, the range where most nutrients stay highly available. Crop recipes narrow it: Cornell runs hydroponic lettuce at 5.8, and UF/IFAS sets tomato solutions at 5.8 to 6.2. Adjust pH last, after every nutrient is in, in small doses, and measure again once the solution has mixed. Expect it to drift up as plants take up nitrate, and check it daily.
What EC should a new reservoir start at?
Measure the EC of your plain water first and write it down. On the Greenway 4-part schedule, seedlings and clones start at an EC of 0.5 to 0.8, rising to 2.0 to 2.5 at peak bloom. For the crop formulas, the university figures cited on the product pages include 1.2 to 1.8 mS/cm for lettuce, 1.7 to 2.0 for cucumbers, and about 2.0 dS/m for young tomatoes, rising toward 2.4. Start at the low end and watch the plants.
Should I top off with water or with nutrients?
When the water level drops and EC rises, top off with plain water. The crop formula pages say to replace the solution on schedule rather than topping it up with more of the formula, since the formulas already supply more of some micronutrients than the recipes call for. The 4-part bundle page calls for a full reservoir change every 7 to 14 days, and Oklahoma State advises replacing the solution completely every two weeks.
How long do mixed concentrates keep?
It depends on the product. The Cal-Mag Plus Safety Data Sheet says to store its mixed concentrate sealed for up to 2 to 4 weeks and to discard it if it turns cloudy or forms a precipitate. The Grow Green, Micro Green, and Blossom Green pages give 6+ months for sealed stock kept cool and dark. The crop formula pages give no storage time for a mixed stock; follow the label. Use opaque, labeled, dated containers, because light breaks down iron chelates.
Review & sources
Written by the Greenway Biotech Team.
Reviewed by Amir Tajer, B.S.M.E., QAL — Co-Owner & Technical Director, Greenway Biotech, Inc. Reviewed against Penn State Extension, The Ohio State University, University of Missouri Extension, UMass Extension, UF/IFAS Extension, Oklahoma State University Extension, Cornell Controlled Environment Agriculture, University of Arizona CEAC, University of Kentucky and NC State University guidance, and peer-reviewed research in HortScience and HortTechnology. Every mixing ratio, concentrate recipe, dose, EC target, and schedule in this guide is taken from the live Greenway Biotech product pages as retrieved on November 4, 2026, with the source each page names; the label on your product governs. Heavy-metal test results are posted on our lab tests page.
Disclosure: Greenway Biotech sells the products named in this guide, including the five crop formulas, Calcium Nitrate 15.5-0-0, Epsom Salt for Plants, and the four products in the 4-part system. Generic pH adjusters and meters are discussed without brand names.
Questions about your water or recipe? Email questions@greenwaybiotech.com or call (562) 351-5168, Monday to Friday, 9 AM to 3 PM Pacific, with your system, reservoir size, and water test.
Sources:
- Hydroponics Systems: Nutrient Solution Programs and Recipes — Penn State Extension
- Hydroponic Nutrient Solution for Optimized Greenhouse Tomato Production (HYG-1437) — The Ohio State University
- Hydroponic Nutrient Solutions (G6984, 2026) — University of Missouri Extension
- Greenhouse Tomatoes: Fertilizing Plants Growing in Soilless Media — UMass Extension
- Nutrient Solution Formulation for Hydroponic (Perlite, Rockwool, NFT) Tomatoes in Florida (HS796/CV216) — UF/IFAS Extension
- Fertilizer Management for Greenhouse Vegetables (CV265) — UF/IFAS Extension
- Electrical Conductivity and pH Guide for Hydroponics — Oklahoma State University Extension
- Hydroponic Lettuce Handbook — Cornell University Controlled Environment Agriculture
- Module 3: Hydroponic Nutrient Solutions (2026 Greenhouse Hydroponic Tomato Workshop) — University of Arizona CEAC
- Hydroponic Strawberry Information: Irrigation — University of Arizona
- Jar Test: Determining Fertilizer Solubility and Compatibility — W. Garrett Owen, University of Kentucky, and Brian E. Whipker, NC State University
- Quantifying the Acidic and Basic Effects of Vegetable and Herb Species in Peat-based Substrate and Hydroponics — Dickson and Fisher, HortScience 54(6):1093–1100 (2019)
- Ferric Ethylenediaminetetraacetic Acid (FeEDTA) Photodegradation in Commercially Produced Soluble Fertilizers — Albano and Miller, HortTechnology 11(2):265–267 (2001)
- Understanding and Applying Chelated Fertilizers Effectively Based on Soil pH (HS1208) — UF/IFAS Extension
Water first, calcium next, pH last.
Ready to mix? Shop hydroponic nutrients
Greenway Biotech, Inc.
- Family-owned In California since 1989
- Packed in Madera, California
- CDFA-registered Fertilizer manufacturer
- Lab tests Heavy-metal results
- Contact questions@greenwaybiotech.com
- Phone (562) 351-5168
- Hours Monday to Friday, 9 AM to 3 PM Pacific
