A UV won't help bacterial infections but I don't think it's a bacterial infection. Most all the bacterial infections are caused by opportunistic pathogens. Meaning they really don't affect fish until they are stressed heavily (i.e. shipping, bad water quality, etc.). So it doesn't make sense that your fish would succumb so quickly to a bacterial infection. My "guess" from what you described would be uronema or brooklynella. Here's some info...
http://www.ultimatereef.com/articles/brooklynella/

A uv wouldn't hurt but I would also do freshwater baths on any fish you have left that look "iffy". Just don't wait till the last second to do a fw bath because once the fish is too far gone it won't survive the bath. I used to give all new fish a 10-15 minute fw bath before they went in the tank. Great way to keep the really nasty bugs out of your system.