Coco growers: how much cal mag?

Hey all. My plants are looking a little hungry for magnesium with interveinal chlorosis on the older leaves. The question is: how much cal mag do you use in your Coco solution, and do you add additional Epsom salts to it?

Thanks OG’s


Set your calcium/magnesium ratios based on potassium. Potassium is an antagonist to Ca/Mg (and the reverse is also true). Coco has a preference toward binding Ca/Mg as compared to K, so it’s a double whammy – takes 1 Ca or 1 Mg and releases 2 K. The K/Ca/Mg relationship is the most volatile part of coco nutrients.

Usually you want between 1.6 - 2x the amount of K as Ca (use 1.6x for soft water and 2x for hard water). If your NPK is 3-1-4 for example, Ca should be 2-2.5. Mg should be referenced as half of Ca, so it would be 1-1.25. Or if you know ppm, then 200ppm K, 100-125 Ca, 50-63 Mg.


Great answer lefthand!

Also I’d add… your water makes a difference as well. I use 2x the amount of Ca/Mg when using RO water than I do with tap/city/well water.


A couple of my favorite links on coco techno…

I use Jacks nutes. No pro. Still learning with each grow.
What type of nutrients are you using? Feed Ph?


I’m using canna nutes at a PH of 5.9 ish. I’m using a potassium based PH down product and I wonder if that will interfere with the uptake of calcium and magnesium?

Potassium based, what’s the active ingredient? I use either sulfuric acid or phosphoric acid.

As for how much cal/mag. Well I grow in coco under cob leds, which supposedly cause their own calmag issues. But I also use very hard tap water, 400ppm from the tap. So it’s hard for me to quantify the proper doses cause even with that hard of water, which is mostly calcium, I still add the recommended doses of cal nitrate and mag sulfate per the Jacks 3-2-1 formula. I actually run megacrop 2 part but it’s the exact same as jacks just with some added aminos.