aquariumfish.net, which I refer to often, says you will eventually need a 29g for dwarf gouramis. If you really want a gouami for a smaller tank, I would say honey gouramis might be a better choice, but those should have at least a 10g tank. 1.5-2g tank really shouldn't be used for anything other than fry or QTing. (I know, I'm a hippocrit because my betta is in a 1g, but I'm working on changing that).