Bleeding Fish! Please Help!!!

I have a 55 gallon cichlid tank. It has three yellow tailed violet cichlids (accei), two red zebras, three baby kenyi and one large pleco. The tank is established, I've had it for about two and a half years. I have onion plants and various other plants. I have a fake stump and a fake tree trunk along with a big treasure vase ornament.

My large yellow tailed violet cichlids started to get this white spottyness to them. Then my large male got this sore in his side and it has gotten worse and started to bleed. They seem to scratch themselves on things, especially the big male. I don't know if he has an external thing that is making him itch and he is just itching himself to death. Maybe he is getting himself stuck in places where he is too big to fit. But both fish have that white spottyness to them. I have seperated the bleeding fish and he is by himself with no ornaments. He also has a white spot under his "chin". Is this a good/bad idea? I've posted some pictures at the below link of the fish and the tank.

Thank you!


http://photobucket.com/albums/b186/palmbreeze2/55 Gallon/

I added some pictures of the white spottyness. It is hard to describe. It isn't like stinking out off the fish. The scales are just this white color. I hope the pictures show it well. The other purple fish is getting a sore on her as well. All the other fish in the tank are fine.

More pics...

http://photobucket.com/albums/b186/palmbreeze2/?sc=3

I think he may have slime disease? I'm going to get some medicine at the pet store today. Should I dose the whole tank? I really don't have anywhere else to put these big fish.

My water is...

KH 14
PH 7.9
Ammonia 0
Nitrites 0

I am dosing with Pimafix and Melafix. My large fish with the sore is still in the aquarium but I seperated him so he wouldn't scratch himself to death.

I have not tested nitrates. Would that really give a fish a disease? I change the water once a week and do a 25% water change. I add Prime at every water change.