I'm not familiar with that - what I would do is isolate the sick gourami ASAP and treat with an anti-internal bacteria med. You can also treat in the tank but monitor the water quality as this kind of treatment may interfere with biological filtration. Do frequent but small partial water changes with de-chlorinated water (replacing dosage as necessary) to keep on top of the water quality. It's best to isolate because this kind of thing usualy isn't easily cured but can easily be passed on to the other fish (as you've discovered). If the fish dies, remove the body IMMEDIATELY.
edit: Oh and don't dispose of any dead fish by flushing them down the toilet etc - rap them in some paper towels and throw them in the trash. Otherwise you can itnroduce common aquarium diseases into waterways where fish don't have any resistence to it.