1. Fix your filter.
There are only 2 ways DE added to a skimmer can return to the pool: something's wrong with your filter OR you have some sort of filter bypass in the piping. Without knowing your filter model (or piping) layout, I can't offer suggestions regarding WHAT is wrong. But I can tell you it's one or the other. If there's no possible bypass to the filter . . . then something's wrong with the filter or the valves on the filter.
2. Fix your chemistry.
DE in your pool does not make algae grow. Inadequate chlorination makes algae grow. So
=> Order a Taylor K2006 test kit from Amazon (links in blue block below), AND
=> Read the Best Guess page, and adjust your chlorine levels based on the info there + testkit results, AND
=> Start adding enough bleach EVERY evening to maintain a DARK yellow to ORANGE chlorine level on a cheap locally-purchased OTO test kit. Do this till you receive the K2006.
=> Report test results from the K2006 here.
=> Don't bother with reporting pool dealer test result. They *typically* mis-report CYA levels, with errors ranging from 50% to 400% (had a 400% one earlier today!).
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