Got a 2 y/o knife fish, approx. 25cm long and has fin rot (treated with pimafix - recommended by aquarium store), however he is also having trouble breathing, swimming around for a short time and then lying down on his side on the floor... he is also not eating which is weird, especially for him. Checked all the paramenters, all fine. Plenty of airation as well. Housed with 2 angels and a royal whiptail. Any advice would be appreciated