I think cory cats and loaches are the best bottom feeders, as the plecos don't tend to do a whole lot of gravel cleaning, at least for me. My shrimp definitely clean up a lot, but they create a lot of waste, ounce for ounce! My tiger barbs so far have not threatened my shrimp, but that may not be typical. Loaches are great but there are some that would get too big for your tank, so look carefully into that (loaches.com).