Dwarf Gouramis may take a bit of time to settle into their tank and establish their territory... when they do the chances are the males will get aggressive. They are generaly ok with anything they do not mistake for themselves.
I (on hearing what peaceful community fish they were) bought 2 male gouramis, by the time they established their territories I had to take 1 back because they were close to killing eachother. Many people suggested I got 2 girls to calm him down which I did. One girl died after 3 weeks of a nasty bite from him the other died after a month of being chased by him. It's all luck I guess.
Just make sure you research well before you buy any fish to save you a lot of time, money and dead fish!
