I observed in my tank today that my male Dalmatian Molly is swimming funny. He sort of swims in a "twitching" matter and it seems at times its hard for him to swim. I am at stage of doing weekly water changes. I have the temperature at 81 and the other fish I have in the tank seem to be fine. Is there anything I can do to fix his behavior, wait it out, or do more frequent water changes?