We have an above ground rectangle pool 20+ feet by 10 ft maybe and 3ft deep. we have had the pool for about 4 years and this year is the first year that we cannot keep the bottom and the corners clean. i am vacuuming weekly and using a push broom to try and loosen the dirt, but it’s just ground into the bottom. we have a salt to chlorine machine, and a sand pump(?). we have shocked the sand by putting chlorine directly into it, but of course that doesn’t do anything for the stains. noticed that the ground in areas are feeling kind of slimy under foot. what do we do?