So my larger albino Oscar that lives in one of my 55s is showing signs of fin rot. His tank mates, male midas and male green Texas are not showing any signs. Qt tank is in use for some new stock so I'm kinda stuck there. Question is, should I move the apparently unaffected tank mates to my other, well established 55 grow out tank? Or do I need to treat the whole tank. Tons of differing opinions on the Internet and I feel like I get consistently well informed answers on here. Just stuck and need some experienced opinions. Been trying for the last half hour to get a pic to upload. Anyways, Allen is showing darkening where he was beat up in the 125. Where his fins were split and down his sides where Brutus tried to skin him. He was showing a great recovery rate until the last couple days when the darkening of the previously injured flesh. Water parameters are ammonia 0 nitrite 0 nitrate ~25ppm. Weekend water changes have been in place and I used aquarium salt to try to help him regeneration the slime coat. Please help! I definitely don't want my other fish sick or exposed to med if it isn't absolutely vital.