Hello, I just noticed my betta has a very puffy gill on one side. The inner bit that normally is tucked up is drooping out, and his scales on the gill are sticking up a bit. I've taken photos but they're too big to upload so I'll add them in a bit. I did a check of water parameters as soon as I noticed. Ammonia, nitrite, and nitrate are all 0 and pH is 7.8 (normal for where I am). He's in a 38L with 5 ember tetras as tank mates. Does anyone have any ideas on what it could be and how I can treat him?