[Plecostomus]

I have found that I usually know more about fish than the Pet store people do(or at least the ones at Petsmart), so I wouldn't completely trust anything they say, although i have gotten good advice before. I think you could have a few more fish, but then you'd have to do more water changes, and nobody wants to do that. I have found that tetras like the cover of plants(live plants are best), if you only got tetras and the betta, you could probably have 8 tetras. I think cories and even Danios could do just fine in a 10g tank, but that's just my opinion.