We recently lost our Honey Gourami in our 20 gallon tank and my father is looking to replace him with something different. Right now the tank has 3 rummy nose tetras, 2 silver tips tetras, 1 head and tail light tetra (reminants of larger schools), one fly fox (or could be a false SAE) and 1 chocolate gourami. We need something that will work well as a single of its kind, not fight with the others, likes plants (not to eat), and gets no bigger than 4 inches. I was thinkign a single male sword would do well, but are they okay to keep by themselves? Any other suggestions?