just an FYI, butterfly loaches need a strong current too... since they come from fast flowing rivers. iv wanted to get some (i actually had some but returned them when i decided i didnt want to build a river biotope) but im afraid it will have to be a project for another day.
depending on how freindly your betta is, you could put a few ember tetras in there. i keep those with one of my bettas and they get along fine. or maybe try breeding cherry shrimp. kuhli loaches would work, though unless you got a school o fthem you might not see them much (and even then i still havent seen my school lately.