The major difference between WalMart bleach and "pool grade" bleach is the price--do yourself a favor and stick with the WalMart bleach. I agree with Watermom in that we can't tell you how high you need to go with the chlorine to shock it without knowing your CYA level. Also keep in mind that if you are killing off an algae bloom, the water will get cloudy as the algae dies, and it requires much filtration in order to remove the dead algae from the water.

Janet