Cal-Mag Plus 2-0-0 Concentrate
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- $ 33.99
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Greenway Biotech · Made in California since 1989
Cal-Mag Plus 2-0-0.
The first pour in every reservoir.
A chelated calcium, magnesium, and iron concentrate built for hydroponics, coco coir, and RO water — the three growing conditions where calcium and magnesium deficiency is most likely. Cal-Mag Plus is the foundation of Greenway's 4-part hydroponic system, CDFA registered and third-party lab tested for heavy metals with results consistently well below required limits.
Find your size → Calculate how much I need3.2%
Calcium for cell wall integrity
1.2%
Magnesium at the core of chlorophyll
0.1%
EDTA-chelated iron, pH 5.0–6.5
35+yrs
Family-owned, California-made
01 / Choose your size
Right-sized for the job.
Each bag dissolves at 2.5 lbs per gallon of water into a reusable stock solution. Finished-solution coverage below assumes a typical mid-range dose of 5 ml of stock per gallon of reservoir; lighter or heavier dosing scales the coverage proportionally.
| Bag Size | Stock Solution Yield | Finished Solution (approx.) | Best For |
|---|---|---|---|
| 2.5 lb | 1 gallon concentrate | ~750 gallons | Small tents, single reservoirs |
| 5 lb | 2 gallons concentrate | ~1,500 gallons | Most popular |
| 10 lb | 4 gallons concentrate | ~3,000 gallons | Multi-tent and small greenhouse |
| 25 lb | 10 gallons concentrate | ~7,500 gallons | Best value |
02 / Ideal applications
One bag.
Six different jobs.
Cal-Mag Plus earns its place wherever the water or the media cannot supply enough calcium and magnesium on its own.
RO & Distilled Water
Reverse osmosis and distilled water start at 0 EC with no minerals. Cal-Mag Plus replaces the calcium and magnesium that purification strips out, typically at the full 10 ml/gal rate.
Coco Coir
Coco's cation exchange sites bind calcium and magnesium, making deficiency very likely even with mineral-rich tap water. Dose at every watering rather than occasionally.
LED & High-Intensity Grows
Intense indoor lighting can raise calcium demand and expose delivery limits during rapid growth. Many high-output LED growers increase Cal-Mag by about 25%.
4-Part Hydroponic System
The first component poured in Greenway's complete feeding program, ahead of Grow Green, Micro Green, and Blossom Green. Dosed 2.5–10 ml/gal by stage.
Foliar Spray
A 5 ml/gal foliar mix can give rapid support for visible deficiency symptoms. Spray at dawn or dusk, and stop foliar feeding about 2 weeks before harvest.
Fruiting Crops
Tomatoes and peppers have high calcium demand during fruit set. Consistent calcium nutrition is research-linked to lower blossom-end rot incidence; it is one input among several, not a guarantee.
03 / Why Cal-Mag Plus
Prevention is cheaper
than correction.
Calcium and magnesium deficiencies are slow to spot and slow to reverse. A consistent low dose keeps them off the table.
3.2%
Calcium for structural integrity.
Calcium is essential for cell wall integrity and may help reduce the risk of blossom-end rot, tip burn, and structural weakness, particularly during rapid growth phases when demand spikes. Because plants cannot relocate calcium once it is deposited, a steady supply matters more than an occasional large dose.
1.2%
Magnesium at the heart of photosynthesis.
Magnesium is the central atom in every chlorophyll molecule. Deficiency shows as interveinal chlorosis, the yellowing between veins on older leaves that moves upward as the plant pulls magnesium toward new growth.
EDTA
Chelated iron that stays available.
EDTA chelation keeps iron plant-available at pH 5.0–6.5, helping prevent the new-growth yellowing common in hydroponic systems. Maintain nutrient solution pH at 5.8–6.2 for best iron uptake; EDTA stability decreases above 6.5.
100%
Fully water soluble, no chlorides.
Cal-Mag Plus dissolves rapidly with minimal residue, making it safe for drip emitters, aeroponic misters, and recirculating NFT systems. It uses pharmaceutical-grade mineral sources with no chlorides and no fillers.
$/gal
You ship nutrients, not water.
Concentrated powder means a single bag can replace many gallons of liquid Cal-Mag at a fraction of the per-gallon cost, with far less shipping weight. Stored sealed and dry, the powder keeps for a long time, unlike liquids with fixed expiration dates.
04 / The science
Why calcium has to arrive first.
Ca2+
Calcium ion — mobile in solution, immobile in the plant
Calcium, magnesium, and iron are the three nutrients most often missing in controlled-environment growing. Base fertilizers are formulated around nitrogen, available phosphate (P₂O₅), and soluble potash (K₂O); calcium and magnesium are frequently left for the grower to supply separately. Cal-Mag Plus fills that gap with a low 2% nitrogen from nitrate sources for immediate availability, plus the secondary and micronutrients a base feed lacks.
The reason Cal-Mag goes into the reservoir first is chemistry. Calcium can precipitate, forming white insoluble solids, when it contacts concentrated sulfates or phosphates directly. Diluting Cal-Mag into the full water volume first means that when later nutrients are added, concentrations are much less likely to reach precipitation thresholds. Use separate stock tanks for calcium fertilizers and other concentrated salts, dilute each independently, and jar-test unfamiliar combinations before injecting.
Once calcium is in the plant it cannot be moved again. Magnesium, by contrast, is mobile and gets pulled from old leaves toward new growth under shortage. This is why deficiency symptoms differ: calcium problems appear in new tissue and fruit, magnesium problems in older leaves. Consistent low-dose feeding addresses both far more reliably than reactive correction.
For deeper coverage, see Why Calcium is Crucial for Plant Growth and our guide to secondary nutrients (Ca, Mg, S).
05 / Application rates
Pick your use.
Get your rate.
All rates use stock solution prepared at 2.5 lbs of Cal-Mag Plus per gallon of water. Always add Cal-Mag Plus to the reservoir first, before any other nutrient.
Stock Solution Preparation
Quick answer: Dissolve Cal-Mag Plus at 2.5 lbs per gallon of warm water to make a reusable concentrate.
| Package Size | Water Needed | Concentration | Yield |
|---|---|---|---|
| 2.5 lbs | 1 gallon | 2.5 lb/gal | 1 gal concentrate |
| 5 lbs | 2 gallons | 2.5 lb/gal | 2 gal concentrate |
| 10 lbs | 4 gallons | 2.5 lb/gal | 4 gal concentrate |
| 25 lbs | 10 gallons | 2.5 lb/gal | 10 gal concentrate |
Note: Use warm (not hot) water and stir until completely clear. A sealed, labeled stock solution generally keeps for 2–4 weeks; discard if cloudiness or precipitate appears. The dry powder itself keeps for a long time when sealed and dry.
Source: Greenway Biotech product label and 4-part hydroponic system preparation instructions.
Dosing by Water Type
Quick answer: RO and distilled water need the full 10 ml/gal; harder water needs proportionally less.
| Water Type | Starting EC | Cal-Mag Rate | Notes |
|---|---|---|---|
| RO / Distilled | 0.0 | 100% (10 ml/gal) | Always required |
| Soft Tap | 0.1–0.3 | 75% (7.5 ml/gal) | Monitor monthly |
| Medium Tap | 0.3–0.5 | 50% (5 ml/gal) | Check water report |
| Hard Tap | >0.5 | 25% or skip | May already supply enough Ca/Mg |
Test your water first: These rates are general hydroponic-practice guidance keyed to starting water EC. Actual calcium and magnesium content varies by source, so confirm your levels with a water-quality report from your utility before deciding whether to reduce or skip Cal-Mag. Coco coir growers should dose Cal-Mag regardless of water hardness because the media itself binds calcium.
Sources: Greenway Biotech product guidance; general university extension hydroponics nutrient-management practice. Confirm against a current water-quality report for your specific source.
Complete 4-Part Feeding Schedule
Quick answer: Cal-Mag Plus runs through every stage, from 2.5 ml/gal at seedling to 10 ml/gal at peak bloom.
| Growth Stage | Cal-Mag Plus 2-0-0 | Grow Green 4-2-6 | Micro Green 2-0-3 | Blossom Green 2-6-8 | EC Target |
|---|---|---|---|---|---|
| Seedlings | 2.5 | 1.25 | 1.25 | 1.25 | 0.5–0.8 |
| Early Veg | 5 | 5 | 5 | 5 | 1.0–1.4 |
| Late Veg | 7.5 | 15 | 10 | 5 | 1.4–1.8 |
| Transition | 10 | 10 | 10 | 10 | 1.6–2.0 |
| Early Bloom | 10 | 5 | 10 | 15 | 1.8–2.2 |
| Peak Bloom | 10 | 0 | 10 | 20 | 2.0–2.5 |
| Late / Flush | 5 | 0 | 7.5 | 15 | 1.5–2.0 |
Note: Add nutrients in order — Cal-Mag Plus first, then Micro Green, then Grow Green, then Blossom Green — and adjust pH to 5.5–6.5 last. New growers should start at the Early Veg rates even with larger plants and increase gradually toward the EC target for the stage.
Source: Greenway Biotech 4-part hydroponic system feeding schedule.
Deficiency Identification & Response
Quick answer: Confirm pH, EC, and root health before raising Cal-Mag — most apparent deficiencies are uptake problems, not supply problems.
| Symptom | Likely Cause | Suggested Response |
|---|---|---|
| Blossom-end rot on fruit | Calcium delivery to fruit | Check pH (6.0–6.5), EC, irrigation consistency, and root health first; consider increasing toward 15 ml/gal only if calcium supply is confirmed low |
| Yellowing between veins on older leaves | Magnesium | Foliar spray at 5 ml/gal for rapid support while correcting reservoir levels |
| Brown leaf tips or tip burn | Possible calcium stress or excess salts | Check EC, pH, and irrigation consistency first; target pH 6.0–6.5 for calcium uptake |
| Yellowing of newest growth | Iron | Lower pH toward 5.8; EDTA iron availability decreases above 6.5 |
Note: Visible symptoms often reflect a pH or root-zone problem rather than a true shortage in the reservoir. Verify pH and EC before increasing nutrient rates, since over-correction can drive EC too high and cause salt stress. Foliar feeding is a short-term support measure, not a substitute for fixing root-zone conditions.
Sources: Greenway Biotech product guidance; general university extension plant-nutrition diagnostic practice. Confirm specific thresholds with a current solution test.
06 / How to use & calculate
Mix it.
Pour it first.
Feed every time.
Cal-Mag Plus is simple to run once the order is right. Use the calculator to get exact amounts for your reservoir, water type, and stage.
-
01
Make the stock solution
Dissolve 2.5 lbs of Cal-Mag Plus per gallon of warm water and stir until completely clear. Store sealed and labeled with the date.
-
02
Add it to the reservoir first
Fill the reservoir, check starting EC, then add Cal-Mag Plus stock before any other nutrient. Stir or circulate before adding Micro Green, Grow Green, and Blossom Green one at a time.
-
03
Set pH last
After all nutrients are in, adjust pH to 5.5–6.5 and confirm EC against the target for your current growth stage.
-
04
For coco coir, feed every watering
Pre-buffer new coco by soaking it in a 10 ml/gal solution, then dose Cal-Mag at every watering — coco continuously binds calcium and must be replenished each feed.
07 / Compare
Calcium sources.
Different jobs.
Cal-Mag Plus is the all-in-one choice when you need calcium, magnesium, and iron together. Other sources are better when you need calcium alone, or a long-term soil amendment.
| Product | Provides | Form | Best For | Notes |
|---|---|---|---|---|
| Cal-Mag Plus 2-0-0 (this product) | 3.2% Ca, 1.2% Mg, 0.1% Fe | Soluble powder | Hydro, coco, RO water | All-in-one secondary + iron supplement |
| Calcium Nitrate 15.5-0-0 | 19% Ca, 15.5% N | Soluble powder | High calcium + nitrogen demand | No magnesium or iron; higher calcium concentration |
| Magnesium Nitrate 11-0-0 | 9.5% Mg, 11% N | Soluble powder | Magnesium-only correction | No calcium; pair with a calcium source |
| Dolomite Lime | Ca + Mg carbonate | Granular / powder | Long-term soil Ca/Mg | Slow-release soil amendment; not for reservoirs |
08 / Decision
Is this the right
supplement for you?
Cal-Mag Plus is built for controlled-environment growing. For long-term soil building, a different product fits better.
Best Choice For
- Growing with RO, distilled, or soft water below 0.3 EC
- Any coco coir grow, regardless of water quality
- High-intensity indoor grows where calcium demand runs high
- Tomatoes, peppers, and fruiting crops with high calcium demand
- Running the complete Greenway 4-part hydroponic system
- Growers who want calcium, magnesium, and iron in a single product
Consider Another Product If
- You need high calcium with nitrogen and no magnesium — try Calcium Nitrate 15.5-0-0 instead
- You only need to correct magnesium — try Magnesium Nitrate 11-0-0 instead
- You want long-term soil Ca/Mg building — try Dolomite Lime instead
- Your hard water above 0.5 EC already supplies enough Ca/Mg — confirm with a water report first
09 / Build the program
Cal-Mag is step one.
These complete the program.
The 4-part system is designed so each component works in balance, from seedling through harvest.
Vegetative
Grow Green 4-2-6
Vegetative growth formula with balanced NPK for healthy foliage through the veg stage.
MicronutrientsMicro Green 2-0-3
Complete chelated trace-element package for enzyme function across the full growth cycle.
BloomBlossom Green 2-6-8
Flowering formula with high available phosphate (P₂O₅) and soluble potash (K₂O) for bloom and fruit.
Best Value4-Part Hydroponic Bundle
All four components together — the complete feeding program from seed to harvest.
10 / Safety & handling
Read this before
you mix.
Cal-Mag Plus is a routine horticultural product, but powder handling and mixing order still call for basic care.
- Wear gloves and eye protection when handling the powder; avoid inhaling dust and use in a well-ventilated area or wear a dust mask. Wash hands after handling.
- Store in a cool, dry place in the original sealed container. The powder is hygroscopic and absorbs moisture from the air, so reseal tightly after each use. Keep away from children and pets.
- Always add Cal-Mag Plus to water first, before other nutrients, to help prevent precipitation. Dissolve in warm — never boiling — water, and rinse equipment after use.
- Never mix concentrated Cal-Mag directly with concentrated sulfate or phosphate fertilizers. Use separate stock tanks, dilute each independently, and jar-test unfamiliar combinations before injecting.
- First aid — eyes: flush with clean water for 15 minutes; skin: wash with soap and water; ingestion: do not induce vomiting, contact Poison Control (1-800-222-1222); inhalation: move to fresh air. Refer to the SDS for complete safety information.
11 / FAQ
Common questions.
Honest answers.
If your question isn't here, contact our team at questions@greenwaybiotech.com.
Why choose powder Cal-Mag over liquid Cal-Mag?
Powder Cal-Mag costs significantly less per dose, ships with much less weight, never expires when stored dry, takes less storage space, and lets you adjust concentration based on your water quality. Because you are not paying to ship water, a single bag of concentrated powder can replace many gallons of pre-mixed liquid Cal-Mag at a fraction of the cost.
Do I need Cal-Mag if I am using tap water?
It depends on your water hardness. Test your starting water EC: water below 0.3 EC generally needs Cal-Mag, while hard water above 0.5 EC may already contain enough calcium and magnesium. A water report from your utility gives exact mineral levels. Coco coir growers should use Cal-Mag regardless of water hardness, because coco binds calcium at its cation exchange sites. For more on calcium nutrition, see Why Calcium is Crucial for Plant Growth.
Can I use Cal-Mag Plus as a foliar spray?
Yes. Mix 5 ml of stock solution per gallon of water and spray in the early morning or late afternoon to reduce evaporation and leaf burn risk. Foliar feeding can provide rapid support for visible deficiency symptoms. Avoid spraying during peak midday heat, cover both sides of the leaves, and stop foliar applications about 2 weeks before harvest.
Is Cal-Mag required for growing in coco coir?
It is strongly recommended. Coco coir has cation exchange sites that naturally bind calcium and magnesium and release sodium and potassium in their place, which makes deficiency very likely even with calcium-rich tap water. Use Cal-Mag every watering at 5 to 7.5 ml per gallon, and pre-buffer new coco by soaking it in a 10 ml per gallon solution before planting.
How do I know if my plants need more Cal-Mag?
Calcium deficiency typically shows as blossom-end rot, brown spots, and tip burn on new growth. Magnesium deficiency causes interveinal chlorosis, the yellowing between leaf veins on older leaves. Iron deficiency appears as yellowing of the newest growth. Before raising your dose, confirm pH and EC, since many apparent deficiencies are uptake problems rather than supply problems. For help comparing calcium products, see What is the Best Calcium Fertilizer?
Why must Cal-Mag be added first, before other nutrients?
Calcium can precipitate and form white insoluble solids when mixed directly with concentrated sulfates or phosphates. Adding Cal-Mag to plain water first dilutes it enough that when you add the remaining nutrients, concentrations are much less likely to reach precipitation thresholds. For unfamiliar nutrient combinations, run a jar test before mixing in the main reservoir.
How long does mixed Cal-Mag stock solution last?
A properly stored stock solution in a sealed container generally lasts 2 to 4 weeks. If you see any cloudiness or precipitate forming, discard it and make a fresh batch. The dry Cal-Mag Plus powder itself has a long shelf life and keeps indefinitely when stored sealed, dry, and away from heat and direct sunlight.
Ready to feed?
Pick your bag. We'll ship it.
Cal-Mag Plus 2-0-0 ships in 2.5, 5, 10, and 25 lb bags, with free shipping on orders over $100 and a 90-day satisfaction guarantee. Start with the 5 lb bag if you are running a single tent or reservoir.
Choose your size →