. I've had a batch of rubber lip plecos in quarantine for a couple of months now. They all look great, but this guy just keeps having trouble with his tail. I've used salt to no avail. The tank is on a drip, which means water quality is good.
Does it look like the fin is "melting" away? I would find that in some of plecos after moving or if they were getting bullied. It just looked like it was receding away. I found water changes in aquarium salt 1 tablespoon to 5 gallons cleared it no problem. I can't really make what that bulge is though