I have had a brown knife for 6 months now with no problems. a few days ago i did a water change 20% as i always do. Now however my knife is covered in a white film, which started out a few days ago as little white specks i thought where parasites. so i treated with ick meds. he is kinda floating, letting his back side sink then swimming again. all my other fish in the tank are fine. I am at a loss. please help, i really like this fish and dont want to loose him but i am at a lose as to what to do for him.