red lump

First time posting. While changing my water I noticed my pleco has developed a large red lump on his side. He's still eating fine and moving around the tank. I've not been able to find other examples so I need to know the best course of action. I have a isolation tank I can fill up if needed.

Hello all,   I've been lurking for a little while but have joined today to ask for help. My bristlenose pleco is about 6 years old and has developed a red cyst on his side (see photo). I've just noticed it as he tends to hide a lot, but I don't think it could have been there longer than 3 weeks...