I got a small flower horn about 4" from a store for a 1.00 they were going to put him down. His tail fin is very thin as you can see in the picture. I believe this to be fin rot . What is the best all purpose antibiotic I could use ? or is this tail issue something else. I have him in a 30 gal tank all by himself. he is eating like a monster and seem to be doing fine except for his tail . any and all help would be great