If there is no excess snow or other debris on your cover, a sagging cover could signify that your cover is improperly tensioned. Make sure that your straps are tight and that the springs are 50-75% compressed. You may need to do some adjustments to bring your cover to the correct level of tension.
If you have a RuggedMesh cover that looks like it is ponding excess water, that’s a good indicator that the mesh could be clogged and your cover may need to be cleaned. To clean your cover, use a soft bristle brush with some mild dish detergent to brush open the pores.
If you have a solid PermaGuard cover with a drain strip, confirm that your water level is 12-18” below the coping. A pump maybe needed to put on the top step of the pool to keep the water level and cover separate. For PermaGuard solid covers without a drain strip, a pump must be used at all times in order to maintain the safety of the cover