What should i do when 1 of my fish lost all its scales and the rest of the fish are losing them too?

Question

what medicine should i use

Answer 1

That would be due to a bacterial infection and best treated with an antibiotic. I wouldn't waste my time with light weight medications, instead go for the better treatments first this time. Marcyn 2 or Maracyn TC would be good choices.

MM

Answer 2

Its probebly too late. There is a fungal infection in the tank. Contact a local pet store and see if they can suggest a cure. Otherwise you will have to boil out the tank and everything in it before you can restock.