Much of the pool industry recommends weekly shocking because they do not understand (or perhaps they do understand but don't want people to know) the chlorine/CYA relationship so they say that 1-3 ppm (BioGuard) or 1-1.5 ppm (GLB) Free Chlorine (FC) is all that is needed regardless of CYA level which can get to 200 ppm which they (BioGuard) say is just fine (but it isn't). The weekly shocking is a band-aid to kill off algae that has started to grow because the FC is simply too low relative to the CYA in the first place. It works for a while, but eventually doesn't work when the CYA gets too high.

Following the recommendations here, including Ben's Best Guess CYA chart, will have algae killed faster than it can grow so will prevent algae growth using chlorine alone with no need for algaecides, phosphate removers, clarifiers, flocculants, or weekly shocking.