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I target K and Ca at 20ppm and Mg at 10ppm.

With a weekly 50% w/c, I initially replenish K and Ca based upon a KH target designed to hit a ph of 6.5, given my current CO2 dosing. I do this based upon the charts, you’ve probably seen them, showing optimal uptake of ferts in the pH 6.5 area AND because 6.5 is about as low as I can go before my ramshorns start to show the effects of acidic water on their shells. So, I use KHCO3 to do this. This usually means that the K target of 20ppm is reached before the necessary KH target.

To complete the KH targeting, I add the necessary bicarbonate with CaCO3, which also adds a good amount of Ca. With a pH of 6.5, the CaCO3 dissolves overnight. If I need more Ca to reach my Ca target of 20ppm, I add it with calcium gluconate (I get enough SO4 from my MgSO4).

I only add about .4ppm Cl to my tank, daily, through an autodoser, which is an inconsequential amount of Ca from the CaCl. I’ve read enough to convince me that staying below 7ppm is possibly the safest thing to do and I do worry a little about the accumulation effects, despite 50% w/c’s. My plants are certainly not complaining about the Cl dosing level. In fact, I recall reading, somewhere, that Cl should be dosed at the same rate that Fe is dosed - true or not.

Summing up; I add KHCO3, MgSO4 and, if needed, Ca gluc to the barrel holding my RO/DI replacement water, the CaCO3 to the tank right after the w/c and the Cl daily through the autodoser along with urea.
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