Okay, I know ammonia should be 0, nitrite should be 0, but is 20-30 nitrate okay? The fish is in hypo at 1.009 refractrometer, 80 temp, last five weeks. I'm just wondering when to do a water change. I do them once to twice a week, depending on nitrates. Should I wait till nitrate reaches 20, 30, 40? The fish is eating and appears healthy and nonstressed and no ich.