I do a 50-70% waterchange every other day straight out of my garden hose; water is cold as hell, it's heavily chlorinated, and probably not the best quality water but all my fishes seem fine, I just dump in 2 caps of prime then fill with the hose. After it fills and hits the sump then the heater kicks in. I keep stingrays and catfish. Maybe fishes are not as sensitive as people think.