Would any other species eat the leeches and the minnows but leave alone the frogs?

I can live with goldfish if the population is controlled. I agree the muck is largely plant debris but the fish aren't helping. I would like to minimize the pond becoming a fish toilet.

I thought of trapping minnows and netting the adults- as many as possible.

In a perfect world I would go back in time and prevent the previous owner from putting them into the pond to begin with. I don't really care if I have fish in my pond.