Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
If the GH is lower than the fish you want to keep, then Seachem Equilibrium is a balanced source of Ca & Mg. It also contains K.
Example: GH of my tap water is usually about 4 degrees. I add Seachem Equilibrium for hard water fish, but not for soft water fish.
If you suspect the GH of your water is entirely from either Ca or Mg, you might just want to supplement the missing element.