I had a dwarf Gourami who sadly died before any other fish in my tank. From what I've read, they tend to be rather sensitive fish.
Could you post your Ammonia, Nitrite, Nitrate and pH values? If you don't have a test kit yet, go get yourself one, they are invaluable for maintaining a healthy tank. Most LFS will test your water for you if you bring in a sample, if you do that make sure you get hard numbers, rather than a general 'your levels look ok.'
Was he recently added, or has he been in your tank for awhile?
When was the last time you did a water exchange? How much water did you take out?
How often do you normally exchange water?
How big of a tank, and what kind / how many fish do you have?
