My pool was built in 1981 and has never had the sand changed.The sand was kinda nasty and when i vacuumed it , the closer i got to the laterals the more it looked like masonry sand.i installed new pool spec.sand,coarse in the bottom and fine on top. I got 5lbs of de that i plan on puttig in tomorrow.Today i vacuumed to waste until i got below the skimmers. I am now filtering from the bottom until it refills above the skimmers again.this is a great site and thanks again for the info.Oh yea ,thanks for the english lesson too....