My betta is still active, excited about eating, and his colors are still bright but there is a weird thing on his stomach. I have tested the water quality and it has 0 ammonia, nitrates are 10ppm, with a pH of 7.2, and I have a sponge filter with a bleed valve (so I can control the flow) and a heater. I have been feeding him frozen bloodworms and I do use fertilizer. Please tell me if this is a sign of some sickness or if it can endanger the life of my fish. Just tell me anything you know about this. Thank you.