Cookieman,

Last night, I dug out the old Monsanto Dequest 2010 -- HEDP -- technical literature I have, and have begun wading through it. Give me a day or two to re-read it, and think about the implications for pool use and dosing. One key element I'm not sure I'd ever noticed before is that high calcium reduces the effectiveness of HEDP. But test conditions were focused on boiler and cooling tower treatment, rather than pool use, so I need to check with Chem_Geek. And, I'm not sure he's ever seen this literature.