Answer:

It depends on the type of chlorine you are using and the concentration of the chemical. There are different types of shock, liquid and granular. Consult the packaging as the dosage should be listed there. It will also depend on the bather load, rain, etc. that introduces contaminants to the pool. The best thing would be to test the water 2 -3 times a week and shock when the free chlorine is 0 or if you have a test that measures both free and total chlorine, shock when the total chlorine is higher than the free chlorine.