Well not really sure how you could get rid of them all together except like you said. Some sort of chemical or put a few adult red ear in there and a few Large Mouth Bass. They both like leeches and would eat most of them but not sure about all of them??? In that small of a pond though I bet the fish would find most of them pretty quick. This is just me but I would rather swim with a few fish then leeches any day!!!
RC
