Help my bristlenose pleco has developed a red lump

[1mightyR]

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.

 

[tylapollyanna]

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.

It looks like a red cyst