Atami - Ata Calmag

A liquid calcium and magnesium supplement for soft tap water, reverse osmosis water and rainwater. Made to bring mineral-poor water up to level before you start feeding.

The first question is not which, but whether

Cal-Mag is one of the most bought additives and also one of the most often needlessly bought. Whether you need it depends not on your plant or your feed but on what comes out of your tap.

Dutch mains water is hard across much of the country. Hard here means: there is already calcium and magnesium in it, sometimes enough to complement your base feed without adding anything. Run on that water and feed Cal-Mag anyway, and you stack calcium into a pot that had plenty, and too much calcium actually suppresses the uptake of magnesium and potassium.

Run on reverse osmosis, distilled or collected rainwater and the reverse holds. Almost everything has been stripped out, including the calcium and magnesium your base feed quietly assumes is there, and topping it up is not a luxury but a requirement.

How to find out without a laboratory

You do not need a water analysis to get a reasonable answer. Two things will do.

Measure the EC of your bare tap water, before anything goes in. Around 0.2 mS per centimetre or lower means soft water and you almost certainly need something. Towards 0.6 or higher means there is already a fair amount in it and you probably do not. In between it depends on your crop and your schedule.

Then look up your supplier's figure for water hardness, given in German or French degrees. That number is public, listed online by postcode area, and barely changes. Both take five minutes and can save you a bottle you did not need.

Dosing

Mix 0.6 to 1 ml of concentrate per litre of water. That range is not arbitrary: the softer your water, the higher in it you sit. On pure reverse osmosis water you start at the top, on slightly soft tap water at the bottom.

Add it to your clean water and mix it through before your base nutrients go in. That way you start from a known base rather than correcting a mixture that is already made up. Usable through the whole life cycle, in soil, coco and all hydroponic systems.

Available sizes

Technical Specifications:

• Type: liquid calcium and magnesium supplement
• Manufacturer: Atami
• Dose: 0.6 to 1 ml per litre of water, depending on hardness
• Intended for: soft tap water, reverse osmosis water and rainwater
• Period: the whole life cycle
• Substrate: soil, coco and all hydroponic systems
• Adding: to the clean water, before the base nutrients

Frequently asked questions

How do I know whether I need Cal-Mag?
Measure the EC of your bare tap water. Around 0.2 mS/cm or lower is soft and needs topping up; towards 0.6 or higher already contains plenty. Your water supplier also publishes the hardness online.

What happens if I feed it when I do not need it?
You stack calcium. An excess of calcium suppresses magnesium and potassium uptake, so you can create a deficiency rather than fix one.

Why is the dose a range rather than a number?
Because it depends on your water. The softer the water, the higher in the range you go.

Can I use it on rainwater?
Yes, that is one of the things it is for. Collected rainwater contains almost no calcium or magnesium.

When do I add it?
Into the clean water, before the base nutrients, so you start from a known base.