I just noticed that my betta has one eye protruding. It appears to be filled with fluid if that helps. He has become lethargic and sits on the bottom of the tank. The water parameters tested fine: ammonia 0, nitrates 10, nitrites 0, ph 7.6, temp 79. It wasn't like that last night. Is there anything I can do for him? What may have caused this? Will he die from it? Do I need to quarantine him?