As JamesW alluded to, I have a QuadDE-100 and I never backwash. I simply tear it down twice per year and clean it. The only time I use my push-pull backwash valve is just before opening it up to clean, I backwash the filter for a minute or so to blow most of the junk off the quad cartridges, then I open it up and clean it all out. It's a lot easier if you backwash it first before trying to lift out the cartridges all loaded down with wet DE. The nice part about not backwashing regularly is that you don't have to guess at how much DE to add. If you tear it down twice per year then you just add the recommended startup amount of DE which, for the QuadDE-100 is 10 lbs. So, every year I use 20 lbs of DE, that's it....no extra DE costs, no guessing, no fooling around with DE every month. The QuadDE filters are amazing in that you can run them quite dirty and not lose flow. To be honest, I forgot to do the cleaning in September of last year and my filter has been running for a year now without ever backwashing....and it still runs fine. Not that I'm suggesting you do that but just to give you an idea for how forgiving these filters are and how bogus the "you must backwash once per month..." claim is made by every pool service guy I've ever spoken to about it....
