I just wanted to share my experience with you guys in case someone has a similar problem. I've had my 4yr old 24" silver aro in his new 225g tank for over 6 mos. Everything was going great and then I noticed that his back, just forward of his tail was floating out of the water. I let it be for over 3 weeks. The situation did not improve, his eating almost stopped and that part of his back was starting to dry out and rot... no fin, no meat, just bone. I knew that I was about to lose my aro and despite several postings here I got no useful info. I went to my LFS and the guy there told me to use METROZEIDENOL at half the recommended dosage, add salt in medicinal quantitiy and raise the water temp a couple of degrees. Repeat the treatment 2 days later with 30% water changes before, between and after treatment. HALELUJAH!!! This guy saved my fish. Three weeks now after the treatment the effected area is all healed up, a new fin is blooming and my aro's appetite has never been this good. Now he pounces on his food like the predator he is rather than me having to hand feed him just so I could get some food in his mouth. I hope this helps.
METROZEIDENOL ROCKS!!