BAD IDEA. I tried it just last week in my 55 gallon tank. The gourami harassed my female bettas, especially two of them, so that they had stress stripes all the time and all but two of the bettas were constantly hiding. The dwarf gourami wasn't violent to them, but kept following them around and touching them with its feelers. It was really funny at first until he wouldn't leave them alone and I saw that they were getting stressed. I had to bring the gourami back to the store. After he was gone all the bettas came out of hiding and were swimming around normally again.