If there isn't a strong current in your tank, I would highly recommend some sort of Nannostomus, especially the smaller kinds like N. marginatus or N. beckfordi. The latter is slightly bigger, but especially the males are very beautiful!
I would go for a large shoal of them, at least 20. add some floating plants if you don't already have them. they swim in the upper and mid section of the aquarium, making them a nice addition to a tank stocked mainly with bottom dwellers. They are ideal, because they have very small mouths! they don't eat eggs or fry, hence they are a common dither fish frequently seen in Apistogramma breeding tanks.

N. beckfordi
N. mortenthaleri is available as well, they are more expensive, more beautiful and grow larger. I have no experience with these so I am not sure if pleco fry are save with these, but I suspect they are!

N. mortenthaleri