Sorry if this is wrong or anything, this is my first time posting anything like this and I'm in a bit of a rush and found this site while googling... My betta fish Larry has this lump around his gill that's been getting bigger and bigger every day. It's actually been there for a while, but it's been getting bigger over the last couple weeks. He's an office fish, and we were told this could be happening because the office's temperature keeps fluctuating, so we put a little heater in it. But it has gotten bigger since the heater's been there, but he seems happy by the heater and eats fine and swims around. Before he had been solitary at the bottom. I also wonder could it be from feeding him too much? Unfortunately I don't know anything about levels.. we change the water 1x a week about 75%. Anyways, I'm worried because it's really awful-looking and is rapidly getting bigger. Could anybody tell me what it is and any way I can fix it? We've tried putting in this blue liquid but I didn't get it so I don't know what medicine it is, I just know we used it to treat pop eye at first. It's Friday at 5 so I'm about to go home but just worried.. I've attached pictures so I hope this helps. Any advice is appreciated. Thank you!!