I have recently lost a Betta and a neon tetra in my small 3 gallon tank, I am afraid I will lose yet another tetra from some disease that I have been unable to identify. I have been using easy strips to check my water, but after the deaths I had it checked by my LFS and they said it only had a small spike in ammonia common after fish have died. But my one of my other neon tetras have begun to show signs of disease. The symptoms are an almost white ring between the dorsal fin and tail, and it appears to be almost decaying around the middle ground between dorsal and tail. If anyone knows what this might be and how it can be treated it would be a great help. I don't want to lose another tetra. Thank you for your time.