Dying angelfish

Question
Hi. I need a help,please. I am discus and angelfish breeder.I keep them together.Sometime my
fish sick and i know what i have to do. But this time cant do nothing. Never had problem
like that before.
I did this mistake 3 months ago. I bought fish from store and dropped in my tank.After 3-5
days this disease started.
I lost for that period 500 -700 angelfishes.And just 1 discus. Don't know why but this
disease kill angelfish ONLY.
Sorry for long story and what i have.
Like example 1 fish.
SMALL FISH.  1st DAY-- stop eating,swimming on the top or hiding.
            2nd DAY-- growing stomach( like ball),rot tail and fin(destruction begins
with a tail fin, swimming like drunk and dead.
BIG FISH : same thing but for 3-4 days.
Thanks for help.  

Answer
Dear k_PoT,
I would do some serious investigative work with your water quality. Test your water for ammonia, nitrite, and nitrate and make sure these levels are all in good order. Make sure the temperature is adequate for the angelfish and non-flucuating.

Are the angelfish fed live food? Maybe that is part of the problem. Live food can sometimes bring bacteria and other illnesses with them.

One thing you should definitely look into is there is a virus that can wipe out whole fish hatcheries. It is known as the Discus/Angelfish Plague....
This could certainly be your problem here....
Here are some links that may help-
http://www.angelfish.net/yabbse/index.php?board=5;action=display;threadid=6391

Unfortunately I've never had any experience with this before. I hope you can get things straightened out soon.

Best of luck and if you have anymore questions, feel free to write!
Karen~