Difference between tank and tap water
My tap water has a KH of 5 or 6 and a Gh of 5 or 6. My tank, which was filled with my tap water only, has a kh of 2 and a Gh of 3. It is about 3 weeks old, I've done a two water changes (10-15%), but the last one (about 8 days ago) killed off almost all my starter fish. The tank is planted with vals, anachris, water sprite, hydro, java moss, anubias, and java ferns. My pH is pretty low (6.3ish). It is a 50 gal long, with an aquaclear 70, flourite and gravel.
I'm curious what has dropped the hardnesses in the tank and whether large water changes with the much harder water would stress fish or plants.