Posted by: m4p But with salt water chlorinated pools, you shouldn't have to shock very often at all.
You don't have to shock often at all in non-salt water chlorinated pools either if you maintain an appropriate Free Chlorine (FC) level relative to the Cyanuric Acid (CYA) level. For manually dosed pools, keeping the FC at least as high as 7.5% of the CYA level will prevent (green and black) alage growth and not require regular shocking nor the use of supplemental algicides or phosphate removers at extra cost. Shocking with chlorine on a regular basis is usually done to make up for having too low a chlorine level compared to the often rapidly climbing CYA level from continued use of Trichlor pucks/tabs.
In a salt-water chlorine generator (SWG) pool, one can usually target a lower FC of 4.5% of the CYA level. However, the standard recommendation of 1-3 ppm FC with 60-80 ppm CYA will NOT prevent algae growth in all pools. With 80 ppm CYA, one should have at least 3.6 ppm FC (4 ppm FC is a safer target).
[Edited on 7/11/2009]