What will break down the muck in my small koi pond that my ducks frequent?

Question

My lined koi pond is around 700 gallons.   My domestic ducks enjoy it very much. A lot of my muck is from their droppings. I have a waterfall and pond skimmer. My filter on the skimmer needs to be cleaned every day (Yuck!) Even then, pond is not clear and there is a lot of sludge on bottom. Would you recommend muck pellets or something else? We are going to drain, clean and refill this spring. Would like to keep it clear this year. Any help is appreciated.