Issues keeping Angels

[rudy]

Every angel I add to my tank seems to develop a strange fin wasting away symptom and eventually die. The fins will start to redden, and eventually start to fray and rot away. I always thought it was something in my tank picking on them until now.

I have tried to treat them, put them in a hospital tank, testing water parameters etc with no success.

My latest is a fairly large Emporer that has started to develop this symptom. As usual eats fine, and is actually in a 150 gallon with no other fish.

Is there anything else someone could point me to as the cause?