ok so i just peeked into my tank and noticed my little orange cobra guppy was acting lethargic and not even attempting to swim. in about an hour or so he will be gone...im soooo sad bc he was so lively and active. he wasnt bullied or anything and is now dying...i just dont understand why! hes been eating and swimming around all day and then boom hes dying...all of my other fish are fine. water stats are good. what could have happened?