i just got a giant platy its the largest fish in my tank it is like three and 1/2" long and it might have velvet or fin rot how would i stop it with out meds?
First step in treating anything is to do a partial water change, up the temp, add salt, and I always put in an airstone (higher temps mean less O2 in the water.)
What specific symptoms is your platy showing? What size tank, tank mates, ammonia, nitrite, nitrate readings? People here can help out a lot depending on how much info they have to work with.