If you don't want to actually weigh the DE powder on a scale, then I recommend going to your local pool store and purchasing a BLUE SCOOP. It is calibrated. Also, unless you take the filter apart and completely clean the grids to remove ALL of the old DE, then you do not need to add the full amount of DE powder. Backwashing does NOT remove ALL of the old DE powder. I discovered this when I removed the top of my filter for the first time after purchasing the house. So much old DE powder (from previous owner) existed that it formed a reverse image of the lid. This was after I backwashed and saw clear water in the sight glass. How do your grids look?