Hi, I'm new here, and fairly new to fish - long story ... Anyway I rescued a pretty goldfish from Wal-Mart (I consider most of my fish purchases rescues!) and it had a small round, red lesion on one side near it's dorsal fin with a white centre that protrudes. I treated the water with Melafix and it seemed to go but today, some weeks later, I notice it's back again. Any idea what this might be? I will try to take a photo later when I have time. Meanwhile any suggestions that I can proceed to investigate would be appreciated! Other fish in the tank seem unaffected, and the fish in question seems happy and healthy apart from this.