I am not a huge fan of the glo fish. My girls picked them out and they are definitely my least favorite in the tank. I guess that could change if we get a few more and they swim together. I will have to see whAt our local pet store has after I get my new tank cycled. It is a pretty small locally owned store, but they carry quite a few different options.
You could always re-home a few fish or keep some in the 10 gallon like the platys. Make some space and you could have a small school of neon tetras. Oh, and i really recommend you re-home your pleco. They get pretty huge and will outgrow a 20 gallon pretty fast.