Having pool balance issues. I have a pop-up pool that is 16X36.?

Right now the pH is above 7.8 and there is no free chlorine. When the water is standing still, it is crystal clear, as soon as the boys jump in, it clouds up and stays that way. I know that it must be sediment on the bottom. We are using the standard pump filter that came with the pool and thinking about upgrading, however, I don't know how a bigger filter will suck the sediment off the bottom of the pool. Any help would be appreciated.