bottom feeder for a pond

Question
well my family has a pond, and we were thinking about
getting a bottom feeder or two, to help keep the bottom
cleaner and not so green, so we could see our gold fish
easier, the pond is around 24 ft wood by 40 ft long and it
averages out about at 16 inches, maybe deeper like 18
inches, we use a bio filter, and about 9500 gallons, i dont
want the fish to be extremely expensive and it would be nice
if it didnt eat our goldfish, the water gets kind of cold,
last year it froze over in the winter, if theres any bottom
feeders that we could get that would help, thanks jonathan

Answer
You're only choice is a high-finned banded shark.  They are not actually sharks.  They are, as far as I know, the only bottom feeder that will over-winter.  It is recommended that you get them in pairs, although I haven't seen any research that scientifically proves this.  They are a bit expensive, at about $45 each for anything over 4", but you shouldn't get them too small as they are a bit temperamental to water chemistry below this size.