I've had my crowntail, Khonsu, for several months now. He was fairly young and in good shape when I got him. About a month ago, I moved him from a smaller tank into a large 5.5 gallon tank. It's heated (75 deg.) and cycled, with several plastic plants and a few other decorations. Ph is 7.0, and I've ordered a kit to test ammonia and the like. I do 50% water changes once a week. He has a peppered corydora as a tankmate. (I know they are usually schooling fish, but he does fine on his own. Betta rarely bothers him.) Recently, the rays on Khonsu's fins have started to look a little more withered than usual. He's still behaving as usual, but I've noticed that two of his rays have lost about half the bottom portion. I think he may have fin rot, but it's very difficult to tell with crowntails. I have Maracyn I and II on hand (which I've read is sufficient if the fin rot is slight.), and Melafix (that I am very hesitant to use...it killed two of my lovely halfmoons.) I use a pinch of aquarium salt and sufficient water conditioner with every water change. I've included a picture, but it's a little hard to see his fins. Khonsu is very friendly and wanted to smile for the camera. Should I go ahead and start medicating with the Maracyn to get a jump on the rot before it gets worse?