Eclipse sand filter? Is that the little round one? There's a fair chance you've lost quite a bit of your sand. If it's a side mount filter, it shouldn't be too hard to open the filter at the top, and check. If you are missing a lot of sand, the algae particles will go right on through the filter (and a skimmer sock won't help either!).

If you want to test your filter BEFORE opening, it, you can add some DE powder -- a couple of quarts -- via the skimmer. If the DE shoots back into the pool, your filter needs work!