@PoolDoc: Good to see you back. I've been concerned about the opacity stochen is seeing. I don't know if it's iron in solution + calcium cloud or iron in solution + algae or just algae. The filter was passing through orange iron sediment and possible calcium before OP started adding DE - enough to noticably reduce flow. It did produce calcium and orange sediment on backwash after adding DE. This pool has seen some periods of low chlorine. I've been reticent to advise shocking the pool for fear of staining - AFAIK there's only been one backwash that clearly produced iron.