I have a question about how much DE to add to an old 36 sq-ft Nautilus filter. My ancient owners manual states 9 quarts of DE, and since 48 oz (volume) of DE is roughly a pound that adds up to 6 lbs. Funny thing is I found a more recent owners manual for a stainless steel NS36 online and that recommends only 3.6 lbs (judging from the schematics it is basically the same filter). I recently manually cleaned the grids and I can tell you that there was a ton of DE at the bottom of the tank, which leads me to believe the 9qts/6lbs is over kill. This time around I back-washed and added about 2.9lbs or roughly 80% of the 3.6lbs recommended in the newer owners manual. I'm just looking for the suggestion from some of the DE filter gurus around here as to what amount works well for you. Thanks.