The fast-acting, fast-dissolving Cal Hypo formula in HTH® Pool Care Shock Advanced 1lb provides chlorination without adding extra CYA for a beautiful sparkle all season. This product is great for all swimming pool types and won't fade your pool liner.

This fast-dissolving formula kills bacteria and algae, reduces chlorine odor and irritation, and quickly restores crystal clarity. Its multi-functional shock treatment for weekly use can solve 90% of pool water problems within 24 hours.

once a week
It's recommended that you should do a pool shock once a week. The more you use the pool, the more often you need to shock it. Occasionally, you may need to perform an extra pool shock after: Heavy pool use, like a pool party.

within 24 hours
The fast-dissolving formula found in HTH shock treatments acts quickly to restore clarity to your water so you can be back in the swimming pool within 24 hours.

Ideally, you should shock your pool at night, so the sun cannot interfere and destroy the active chemicals before they can do their job. Then, you can add your chlorine post-shock after the chlorine levels have fallen below 5 ppm.

Our best overall pick is HTH Pool Care Shock Advanced, which you can use in most types of pools and doesn't raise CYA levels. It's a granule formula that is also easy to apply, though you may need to use a brush to fully dissolve the product.