Clean pressure is different for different filters. Contrary to popular belief, you should never have to replace the sand unless you really get it gunked up (Baquacil conversion, overkill on suntan lotions and oils, etc.). One or more of our mods is going over 10 years with the same sand! You don't really need to use anything to clean the filter, except backwashings when the pressure indicates. You need to backwash when the pressure rises 6-8 psi over your "clean" pressure. As long as it's doing an effective job of keeping your water clean, then you're good!

I do agree with Anna that you can cut your pump run time from 24 hours to something shorter. In my pool, 6 hours or so daily (26K gallons, 300# sand filter) works, but to make it easy during the summer I just turn it on when I get up in the morning and turn it off sometime after dinner