Nano fish that swims in open, top half of tank?

[lastlight]

As the title states I want an active small fish for my 34g cube to add some energy to the tank.

Any ideas? Current tankmates are a bicolor blenny that hides in his rock most of the day, a neon goby that perches, and 2 chromis that swim a fair amount but like to also hang out close to the rocks.