Generally speaking, pool owners using chlorine based shock will shock the pool every other week EXCEPT in the “extreme” conditions: extreme heat, extreme rain and extreme bather load (like a big party). In these cases, shocking can become more frequent, maybe once a week. We try to teach our customers to pick a night (garbage night? Sunday night?) and get on a schedule. Shock should be added after the sun goes down (not necessarily at night but when the sun it not at its peak and not beating down on the pool) and then allow the pump to circulate the water over night or for at least a few hours after adding the chemical. For those customers who have an ozone system, shocking is less frequent.