I'd also concur with both Harlequins and Rummynose tetras. I've had Harlequins before, quite beautiful fish although once they become used to their surroundings they tend not to school so tightly.
I currently have a school of 8 rummynoses in my 30g and they are great schoolers, when their color is up they are fantastic to watch!
I currently have a school of 8 rummynoses in my 30g and they are great schoolers, when their color is up they are fantastic to watch!