HI. I have a large in ground pool with a sand filter and like to shut down the filter at night to save electricity. Recently, when I re-start the pump in the AM yellow debris re-enters the pool for the first 2-3 minutes. Now I am vacuuming far too often. I always backwash after vacuuming and when I re-start the filter after completing the backwash, the water is clear when it re-enters the pool. I have lots of trees around the pool. My sand filter is at least 30 years old.