Please Help My Sick Black Moor!

Question
I have a 55 gallon community tank with 5 fancy goldfish and I have had one of them, a black moor named Skitzo, for over 9 months. Last night before I went to bed, i saw that he was perfectly fine, then today when I came back from school I saw that his belly had gotten white with some sort of decay and that all his fins have been badly damaged! I can guarantee you that this happened in less than a DAY! I don't know what it is, though I know that the white "decay" isn't white little spots like ich, however, I have no idea what to do to treat him! I checked the ammonia,nitrate and nitrite, which are at 0 ppm and put him in a hospital tank immediately. Is there anything I can do to cure him? I don't want to lose him!!!
http://i30.photobucket.com/albums/c329/xifaur/Picture0137.jpg
http://i30.photobucket.com/albums/c329/xifaur/Picture0140.jpg

Raul
P.S. Thank you so much for taking your time to help us out!

Answer
Raul,
I recommend keeping him in the sick tank - very good idea - and keep a close eye on him for the next week. Start treating with LifeGaurd - a remedy that cures a number of diseases while being safe for fish who are not sick as well, and do small frequent water changes every day or every other day until he begins to recover.
While doing this, make sure do do the same for your main tank, because if one fish got sick there is a very large possibility your other fish will get sick as well.
Thank you for the pictures, and it seems to me this is either a bacterial infection, or possibly parasites. Both of which may be treated by LifeGaurd - which can usually be found at stores such as PetSmart.