I have 2 neon tetras and 1 black tetra, as well as 2 cory catfish (1 leopard, 1 albino). I suspect that 1 of my tetras is a female, and her belly appears to be swollen. I’m thinking she could be pregnant, but more likely sick, and a male keeps nipping and butting her. I have a 5 gallon aquarium, and I’m wondering what I should do to prevent the situation from getting worse. I heard that 3 tetras is too few and they are glass surfing and crowding at the back of the tank, but I already have 2 Corys, so I’m thinking getting 3 more tetras would be overstocking the tank. I replace 1 gallon of water regularly and vacuumed recently after a long time.