I'm gonna echo what Poconos said above --- I also don't think it is a sand problem. You can certainly try backwashing the filter and then when it is clean, note your filter pressure. Do the DE addition - slowly - only adding enough to raise the pressure 1 psi. It may take a half hour or so to see any change in pressure. Adding just a little DE to a sand filter helps it to catch and filter out the smaller stuff that the sand alone might not get. It might be the very thing to solve your cloudy water problem. Also, while you are trying to clear it up, run the pump 24/7.

Post your numbers and somebody here can take a look and see if there is something else we can offer to help.