It is generally recommended to secure a pool cover as firm as possible. It should be drum-tight in appearance, though a minimal indentation in the middle is allowed. If you fail to secure your pool cover properly, the whole structure can end up being too loose which allows debris to enter the pool itself. Keeping your pool water at an optimal level when it’s covered is also vital for successful preservation. The pool water should not be too high, especially in spring and fall, since the pool cover gathers more leaves than it normally would, resulting in the cover sagging lower. When the pool water level is too high, the accumulated leaves will simply stagnate in the depressing cover which can eventually lead to mildew growth and unpleasant odors. But avoiding high water levels is not enough to prevent possible problems since too low levels can also cause damage. It is generally recommended to keep your pool water level at 18 inches or slightly higher from the top of the pool. When you drain your pool too much or perhaps don’t fill it enough, the water level falls below 18 inches from the top, putting a strain on the pool cover. This causes the cover to stretch, sometimes to the point of tearing. Aside from ripping, this strain can lead to the anchors that hold the cover tight to become dislodged from the pool deck, resulting in the collapse of the entire structure.