Aggressive dwarf gourami

[trampoline98]

I have 2 dwarf gouramis(one fire dwarf and one powder blue dwarf), and the slightly larger fire dwarf gouramI constantly chases the other around. They are in a well planted, 20 gallon tank with plenty of hiding places, etc. What should I do to stop this?

 

[Butterfly]

Gouramis are frequently aggressive to their own species. Is their any physical damage being done? Is the one being chased showing stress?(pale color, not eating, hiding). You may have to move one of them if so.
Carol