I have a pictus catfish...he is happy and healthy living in a 90 gallon aquarium with FW cudas and i have never had a problem...every one minds there own business.....so i thought i would get the little guy a friend....so i got anothr pictus and quarintened it for a few weeks and then added it to the tank....which in 2 days he developed a bad case of fin rot...in a matter of a few days all the poor guys fins were at least half gone.....so i ripped my tank apart....removed the unhealthy catfish...treated the tank to protect the otehr fish and then put the sick guy in a hospital tank full of chemicals....lol....and in a week all his fins grew back and he was healthy again.....i left him in there for 2 months to be positive he was 100 % and then a few days ago i reintroduced him to the tank...and here we are 3 days later and his fins are rotting away again...yet the other pictus is fine??? Can anyone help me here.....what should i do about this