We discuss with customers the importance of removing the excess water from the pool cover, but I think we need to make people mindful of removing excess leaves as well. As leaves break down they begin to release tannic acid, the same acid that is released in tea leaves. Once the leaves fall and begin to degrade they begin to release the tannins. If you have a permeable cover (water can pass through) then you in essence have a giant teabag steeping into your pool. To prevent spring staining, and improve water clarity at time of opening remove the leaves periodically from the cover.