I keep 2 Dwarf Gouramis in a 55 gallon heavily planted tank with my Rainbows; they don't "get along", but because there is alot of hiding room (i.e. - areas to create "territories"), they coexist OK. I would suggest you move up to a larger tank when you can. A 30-gallon high has the same base as some 20-gallon tanks, and you can find them cheap on Craigslist pretty often, if you live in a decent size city. Room for the fish to have their own space really helps with the Dwarfs. For best results, go even bigger.