What size tank?
Is it cycled?
How long has it been set up for with fish?
What other fish are in it?
What are your ammonia, ntirite and nitrate readings?
If you don't know what cycling is or are trying to cycle with the dwarf gourami, you need to abandon this attemp. take the gourami back to your fish store and read the links in my signature so that you can begin a fishless cycle.
Dwarf gouramies are exceptionaly prone to disease. Yours is developing an ulcer. This can be caused by a virus - which is untreatable - or bacteria. Most probably the problem is the virus but it is worth purchasing some anti-bacterials to prevent secondary infections. If the water quality is good and your gourami doesn't contract any secondary infections, it could possibly recover - though chances are it won't and, if your tank's not cycled, it definitely won't.
