Well you better find the loach, you dont want a dead fish lying around in there to mess with your water chemistry.
Well, I would have to say a clown pleco would do grand in a tank like that.
hmm. I seem to have one that has outgrown my tank, I will drive it over immediatly.
But if you dont want it I have a Rapheal Talking Catfish, and they do wonders, I had a rock completely covered with algea, within days it was scrapped bare. What type of bottom feeder are you looking for, algea, excess food, whatever?