For some reason my paradise fish has started behaving strangely. It will sort of twitch or recoil slightly every few seconds, as though it suddenly saw something in front of it. Then other times it will flip round and swim off a bit. Any ideas what might be the problem? Ive had the fish for over a year and it has been fine all this time, though i did originally have 2 but just recently got rid of one as they were getting too aggressive with one another.