If this is a Zodiac Duoclear (or if you have the Nature2 system by itself), save yourself the $100 per season for the cartridge and just remove it (if it's the Duoclear, you can open up the cartridge, remove the "mineral" bag and replace the empty cartridge into the Duoclear unit - a cartridge has to be there or the thing will leak). Then run your chlorine level at the reommended level based on your CYA level (for salt water pools), instead of the ludicrous 0.6 level suggested by Zodiac.

All I use in my pool with a Duoclear (mineral bag removed last year) is salt, and muriatic acid to lower the PH level (and bleach when I open after winter to shock the pool). Since I lowered my TA to 70-80, the PH rise slowed markedly. After I added borates, the PH seems to be locked at 7.6.