My son has 7 (soon to be 3) ducks that he built a pond for. As usual, he got himself into something without doing research so now it's my job to try to figure out a plan to filter it. From what I've seen, there doesn't seem to be a store bought filter that will do the job well enough. I told him it seems that pumping the water out (he already has a good pump) every so often seems to be the best solution. Am I right and how often should he do it? I'm not good at sizing something so I'll post a pic. About half of it (maybe a little less) goes down about 2 feet. The other half gets more shallow.