I don't know. There is so much conflict on this subject it's like religion versus evolution. I got ich as soon as I started my system. I placed all fish in hospital with copper and hypo for 4 weeks while leaving the main tank go fallow. Didn't work. fish went back in hospital, this time for 8 weeks while main tank go fallow. Didn't work either. Now I just try to manage and stay on top of these nasty little bugs. Still fighting it. So far no loss of life.