I have a ten gallon heated tank that is divided into three sections.
First one: My betta in the middle refuses to eat anything. She goes to eat whatever I put in, then spits it out. I have tried Freeze Dried Bloodworms, some weird blood worm stuff that every other fish eats up, betta pellets, and fish flakes. She has been like this for months. Started a few weeks after I divided the sorority.
Second one: She is all the way on the left. No eating issues. She loves her food, and even jumps for it. She just looks like she has a tumor. It's been noticiable for a month or two. I noticed it when doing my yearly redecorating for my tank. I clean the whole tank out and run everything under hot water. Except for the filter cartridge. She used to have permanent stress stripes, but amazingly, they are gone now that the bump has appeared.
Third girl is in perfect health. She has eye issues since the other girls used to attack her when they were in the sorority.