A week or two ago I went away for a week. The tank had a water change (at most) a week before that. It usually gets a weekly 10% change, or, if I'm busy, a fortnightly 20% change. I had someone come in and feed the fish twice that week. When I came home I found the tank was pretty dirty (a lot of algae on the pebbles) and so did a 20% water change immediately and have kept it clean since. I noticed my fighter (about a year old now) had a large red bump (a bit smaller than his eye) in between his right eye and nostril (?). A few days later it became a crater. It looks like the bump (cyst??) had burst, leaving a red ring. It is still raised above the skin, it doesn't look like it has eaten away his actual body, it's just a red raised ring. It looks like it might be going down very slowly but that could be wishful thinking - hard to tell. No other symptoms at all apart from a slight change in behaviour - he seems to be flaring his gills a lot more often than he used to. I've considered that it might be because the lump obscures his visions lightly and he might be chasing away whatever it is he sees? Maybe? He eats just fine, he's a big, fat boy (I feed him well) and he's just as happy as ever. No white spots or anything that looks fungusy. Any ideas???? Can I do anything to help him?? 65L tank, plants present (hardly), ammonia and nitrite 0, ph 7.6-7.8 (I moved house a month ago, pH was 7.4 where I lived before). Lives with: 7 black neons 1 three-lined catfish (I plan on buying more - if it safe to??) 1 western pygmy perch 1 mystery snail I have very limited internet access so might take a while to respond to any further questions. I don't have a photo. I will try to take one, but it will take me at least 2-3 days to get it on here. Thanks!