Thank you for your help! I have used nothing in the pool but 6% bleach, Borax, baking soda and granular stabilizer. My filter runs about 7.5 lbs of pressure after a backwash and doesn't really seem to rise very much even after vacuuming or letting it run for a week or more. I have back washed about once a week or so even though the pressure doesn't really seem to rise more than a pound or so.