I'm pretty sure a clown fish I bought a couple days ago has fin rot. Looked fine when I got it, has been eating and swimming normally. Started to see some damage to the tail fin, damage as in splitting/degeneration. Today the damage has rapidly progressed and the tail fin is almost gone. There's a very sharp horizontal line of ok and not ok color. From what I've read it sounds like rot. The only other fish is another clown, but they seem to have been getting along fine, they're both pretty young, and the other one thats been in there a couple months is very healthy. I think the stress of a new tank did it. My question is is there any way to help the situation without antibiotics, which id rather not use. My parameters have been stable.