Whoa! Loaches get quite big, I am sure. I think they can grow to several inches? Then again I could be wrong. *Googles Kuli Loaches* Yup, they get 3-4 inches long. Too big for a 10 gallon, let along 5 of them. Maybe a nerite snail or two. They can eat the stuff, have a little more bio load than a fish, but are smaller and more manageable. Also, they can't spawn/breed/reproduce in fresh water as their eggs require brackish water to mature and develop.
Or perhaps shrimp? Don't go with the overly expensive and rare ones. Chances are you'll loose them to the betta so you don't want him eating a large chunk of change via an animal that way.