Do not put DE into the sand filter as it is filling with sand. Only use pool filter grade sand. You need to partially fill the filter with water before you add the sand, then when you add the sand be careful not to break or crack any of the laterals--those little "fingers" that stick out from the center. When you get ready to start up the pump after the filter is filled with sand, MAKE SURE YOU START IT UP IN BACKWASH MODE. I learned this the hard way, and it took weeks to get my pool cleared up again!!! Let it backwash all the little fine dust out before you switch it to rinse and then to filter. Remember not to switch positions on the filter with the pump running--you must turn it off before changing positions.

Later on, if you find that you're having filtration issues, then you can add a little bit of DE to the filter to help catch the smaller stuff--but it washes out when you backwash, so it's a repetitive thing.

Janet