Are the patches fluffy/fuzzy? Almost like bits of cotton?
To me, it looks like Columnaris. This is a bacterial infection. It's common in fish that have been recently subjected to stress.
What is the water temp? If possible, I would lower it to about 76F. Lower water temps slow down the bacterial growth rates.
Do more frequent water changes. This physically removes bacteria from the water.
You can try the salt treatment that PetMania recommended. Salt has mild antimicrobial properties. However, I personally don't like using salt, as it can stress the kidneys, and lead to other issues (such as bloating, or buoyancy problems). If you decide to use it, I suggest just a day or two, and while monitoring the situation.....
Columnaris can be aggressive. If water changes, lower temps, and salt aren't effective, I would:
a) Do a 100% water change to remove bacteria (as well as any salt that you've added).
b) Treat with an antibiotic that targets gram-negative bacteria. My preference for Columnaris is the furan class. Any one of these three will work: API Furan 2, Bifuran, Jungle Fungus Clear. (Fungus Clear is available at Walmart.)