Hi, I noticed after cleaning my bettas tank that he has a pale yellow spot on the back of his pectoral fin, it looks like you could pop it or like a blister? Could he have hurt himself? It's a 16 gallon ammonia 0 nitrite 0 nitrate 5, 50% clean every 4 days shares his tank with his snails. Does anyone have any idea what it could be? He's still happy eating etc.