HI all! I’ve had my red devil for about 6 years now and have never had an issue with him. He lives in his own in a 100gal tank. As of Saturday he developed this after have a somewhat swollen eye for about 4 months now. When it first started to pop I did water change after change and treated for popeye but never changed. I just assumed it was going to be that way now because he was eating and acting totally normal. Well after a very small water change on Thursday, the following Saturday his eye became swollen and cloudy and had a bubble on it. He is acting normal and eating. I’m going to do a 50% water change and change my carbon to a more intense one that cleans inorganic and organic materials. I’ll post some pictures. I was wondering if it was gas bubble disease but he only has the one bubble on his eye. Any ideas?