I bought this betta fish about a week ago and put inside a 10 gallon community tank. The tank is filled with platys, guppies, corys, and danios. All the fish are very healthy and have no diseases. A couple days ago, I noticed that his fins were changing into a crowntail betta’s. I looked online and saw that it could be fin rot. I already have aquarium salt in the tank(I always have it) and the temperature is perfect. Water quality is also good. Any ideas?