1 L bottle of Calcium Magnesium supplement, NPK 2-0-0 label

500 ml bottle of liquid calcium-magnesium supplement for hydroponics

5 L container of CalMag with eye hazard pictogram

CalMag range in three sizes, 500 ml, 1 L and 5 L

10 L container of calcium magnesium supplement, blue label and black cap

Liquid calcium-magnesium supplement for hydroponics

$17.00

Packaging	Price	Price per L	vs 500 mL
500 mL	$17.00	$34.00	—
1 L	$23.00	$23.00	−32 %
5 L	$59.00	$11.80	−65 %
10 L	$115.00	$11.50	−66 %

$5.66 × 3 with no fees Klarna.

This liquid supplement provides soluble calcium and magnesium to crops that are deficient, whether grown in reverse osmosis water, coco fibre, or with a low-calcium fertiliser. It is dosed at 1.5 ml per litre of solution and will not block drippers.

Ref. TA-CALMAG-500·Hydroponic fertiliser

Packaging : 500 ml

500 mL

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Delivery within 2 to 15 business days

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The summary

What you receive: a bottle of liquid NPK 2-0-0 supplement, with 4% calcium oxide and 1% magnesium oxide.
When to use it: with reverse osmosis water, in coco fibre, or alongside a low-calcium fertiliser, to treat a confirmed deficiency.
The dose: 1.5 ml per litre of nutrient solution, 2 ml with reverse osmosis water.
How to choose: the comparison tool shows how it compares to Epsom salt, which supplies magnesium without calcium.

Soluble calcium and magnesium for RO water, coco fibre and hydroponics

Calcium and magnesium are two secondary elements that a hydroponic crop can run short of, because very soft water supplies almost none and some fertilisers contain very little. This liquid supplement delivers them in a fully soluble form that plants absorb easily and that leaves no deposits in drippers. You add it to your usual nutrient solution at the same time as the fertiliser, whenever your water or grow medium calls for it.

🧪 Two elements, two roles

Calcium

It builds cell walls and strengthens plant tissue. A deficiency scorches the edges of young leaves and blackens the tips of fruits.

Magnesium

It sits at the centre of the chlorophyll molecule and aids phosphorus transport. Its deficiency yellows the older leaves first, between veins that remain green.

These two symptoms do not appear on the same part of the plant, which allows you to tell them apart. Magnesium is a mobile element: when it is lacking, the plant draws it back from older leaves to feed new growth, so yellowing starts at the bottom. Calcium, by contrast, stays fixed where it has been deposited, and its deficiency affects organs that are still forming, young leaves and the tips of fruits. On a tomato or pepper, blossom end rot is the most familiar form of this.

💧 Dosage based on your water

The standard dose is 1.5 ml per litre of nutrient solution, suitable for most crops and even the most demanding plants. With osmosis water, which contains almost no minerals, the dose rises to 2 ml per litre. For a 30-litre reservoir, you would add 45 ml, and a one-litre bottle covers just over 22 fills. The supplement should only be used when a recognised deficiency is present, never as a matter of routine, since an excess of calcium and magnesium inhibits the uptake of potassium and iron. Always check the pH with a drop test kit before dosing, as calcium is only properly absorbed above 5.8: bringing the solution to around 6.5 is sometimes enough to stop new symptoms appearing.

Supplementing an organic fertiliser with osmosis water

The mineral fertilisers in the range are available in a soft-water version that already supplies calcium, whereas a liquid organic fertiliser such as Pro Organic Grow does not guarantee this. With reverse-osmosis water, which contains virtually none, the application chart therefore pairs this supplement with the Pro Organic programme, at a dose of 2 ml per litre in RO water. This way you keep your crop on an organic fertiliser programme, with the calcium and magnesium that your water does not provide.

No supplement needed with soft water formulas or NovaMax

The soft-water versions of TriPart and DualPart, as well as DualPart Coco and NovaMax, already contain the calcium required, including when used with reverse osmosis water, and this supplement should not be added to them. In hydroponics, excess calcium can react with the sulphur in the solution and form a deposit at the bottom of the tank. If this occurs, clean the tank before preparing a fresh solution. The liquid causes serious eye damage: wear eye protection when measuring doses.

🥥 Starting out with coco coir

Coco fibre absorbs some of the calcium and magnesium from the solution passing through it, particularly during its first wetting. If you are preparing it yourself with a fertiliser from another brand, soak it to saturation with water dosed at 1 to 1.5 ml per litre, then maintain the same dose in your solution for the first two weeks. For fast-growing plants, supplementation can continue beyond this point. The 50 L bag of coco fibre from the shop arrives pre-rinsed and stabilised, and can be used straight away.

Technical specifications

The formula

Declared formula: NPK 2-0-0Two secondary elements and a small amount of nitric nitrogen
Total nitrogen: 2.5%, nitric
Calcium: Calcium oxide, 4%Water-soluble
Magnesium: Magnesium oxide, 1%Water-soluble

Use

Standard dose: 1.5 ml per litreFor most crops and heavy-feeding plants
Osmosis water: 2 ml per litre
Solution pH: 5.5 to 6.5Below 5.8, calcium is less readily absorbed
Storage: 5 years after openingKeep tightly sealed, away from frost

Safety and bottle

Ranking: Danger, H318 hazard statementSerious eye damage: wear goggles when measuring doses
Standard: Regulation (EU) 2019/1009Simple liquid inorganic fertiliser with macronutrients
One-litre bottle: 21.6 x 8.9 x 8.9 cm
Manufacturing: France

To budget for separately

pH control: A pH test kit in drops
Monitoring magnesium: A magnesium test

6 further specifications are available in the detailed view.

In the box

1 bottle of calcium magnesium supplement, in your chosen size: 500 ml, 1 L, 5 L or 10 L

Composition, doses, pH range, standard, shelf life, and dimensions recorded on 01/10/2026 from the product data sheet and the manufacturer's safety data sheet.

Calcium and magnesium, or magnesium alone?

Two inputs that complement each other but cannot replace one another. The first is dosed into the nutrient solution, the second is sprayed onto the foliage.

Are you unsure between these two inputs? One supplies calcium and magnesium to the solution, the other magnesium and sulphur to the foliage. Three questions are all it takes to decide.

	Elements supplied	Shape	Nitrogen	Primary use	Calcium
Recommended Liquid calcium-magnesium supplement forYour choice	Calcium and magnesium	Ready-to-dose liquid	2.5% nitric	Nutrient solution, RO water and coco	Yes
Epsom salt, soluble magnesium sulphateYour choice	Magnesium and sulphur	Crystals to dissolve	None	Foliar spray	No

Liquid calcium-magnesium supplement forRecommended

Elements suppliedCalcium and magnesium

ShapeReady-to-dose liquid

Nitrogen2.5% nitric

Primary useNutrient solution, RO water and coco

CalciumYes

Epsom salt, soluble magnesium sulphate

Elements suppliedMagnesium and sulphur

ShapeCrystals to dissolve

NitrogenNone

Primary useFoliar spray

CalciumNo

Compositions and usage figures taken on 01/10/2026 from the manufacturer's data sheet and from the shop's Epsom salt data sheet.

Documents & manuals

Safety data sheet, in French

The data sheet details the composition, hazard statement H318 and first-aid measures in the event of splashing in the eyes.

PDF · 0,2 Mo

Download

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delivery time

Liquid dispatched by tracked parcel from France. Exact shipping costs and final delivery times are displayed at checkout once your address has been entered. Outside the European Union, import duties and taxes are the responsibility of the recipient.

Frequently asked questions

6 questions

6 key questions

How can you tell if calcium or magnesium is lacking?

Start by looking at which part of the plant the symptoms appear on.

A calcium deficiency scorches the edges of young leaves, distorts new growth and blackens the tips of fruits.
A magnesium deficiency causes yellowing between the veins of older leaves, which remain green.
When both appear together, the cause is often RO water or unprepared coco fibre.

A magnesium test confirms the second case before you dose.

What dose for a 50-litre reservoir?

Can it be added to a TriPart fertiliser?

No, neither with the soft-water versions of TriPart and DualPart, nor with DualPart Coco or NovaMax, all of which already contain sufficient calcium, even when used with reverse osmosis water: this supplement would create an excess that hinders the uptake of potassium and iron. With these fertilisers, it is only useful to correct a hard-water version used by mistake with soft water.

Is it suitable for organic farming?

I've added the supplement and the deficiency persists — what should I do?

Check these four points in order, as the cause is rarely a lack of calcium in the water.

The roots must be white and firm; otherwise they can no longer absorb anything.
A pH that has dropped below 5.8 should be corrected back to 6.5.
Air humidity should remain between 50 and 70% during the growing phase, as air that is too humid slows transpiration and, with it, the transport of calcium through the plant.
An excessively high temperature also blocks calcium uptake.

How long does the bottle keep?

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Liquid calcium-magnesium supplement for hydroponics

The summary