Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Figure out what GH is best for the livestock.
Soft water fish are generally best with GH in single digits (under 9 German degrees of hardness) and lower is better. A good target is 3-5 degrees.
Set the KH about the same.
Do this when you do a water change, then monitor it through the week.
If the plants are using so much of either Ca or Mg that the GH is dropping, then you might want to supplement it mid week. I have never had to add this mid week. Once a week, with the water change was enough.
Some substrates remove the carbonates from the water, so there are a few tanks where I have supplemented the KH mid week. (potassium bicarbonate or baking soda)
Good that you are supplementing both Ca and Mg, not just one or the other. Have you done a Ca test so you know what ratio to add these?