Hi...I disagree. I think water changes are extremely important when treating some types of fish diseases. This is probably one of those times when your fish are most stressed. Water changes remove any toxins (nitrate), return minerals and keep the water as fresh as possible. In addition, you may even help a bit by removing some of the organism itself. When humans take medications, they have peaks and troughs (dips) in their medication levels. Water changes shouldn't effect the efficacy of the ich medication if you follow the instructions on the label. I've had 2 successful ich treatments. I did daily 10% water changes (before dosing the tank). The mainstays are raising tank temp, removing the charcoal from the filter, using the appropriate medication and dosing as per instructions, treating for 2-3 days after the last spot disappears. I hope this helps. Sh