How about 1 other single fish that swims the top? I notice that the tiger babs always swim in the middle- lower areas and would like one to swim the top area. I had barely got 8 green tiger barbs to go in with the 11 normal tiger barbs and the green ones are very little
As the barbs get larger (their adult size is actually larger than what many people think), I think they'll fill the entire tank. So I wouldn't add anything else that would swim in the same level as them.