Ammonia can irritate their skin so do a 75% water change and gravel clean the substrate each day until the ammonia is 0.
Reduce feeding to once every second day until ammonia is 0.
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How long have you had the fish for?
Have you added anything new to the tank in the last 2 weeks?
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If you shine a torch onto the fish that are rubbing on things, and it shows a gold sheen, the fish have velvet (Oodinium).
Depending on what other fish are in the tank, you can try increasing the water temperature to 30C (86F) and keep it there for 2 weeks. Increase aeration if you do this because warm water holds less oxygen than cool water.
Before you increase the temperature, wipe the inside of the glass, do a 75% water change and gravel clean the substrate, and clean the filter if it hasn't been done in the last 2 weeks.
