About This Item HTH Shock Advanced is the powerful 4 in 1 formula with Cal Hypo that kills and prevents bacteria and algae as well as reduces chlorine odor and irritation for crystal clear healthy water. Traditional chlorine products contain cyanuric acid CYA. When too much CYA builds up it can cause overstabilization or chlorine lock and cloud your water. The fast acting fast dissolving Cal Hypo formula in HTH Shock Advanced provides chlorination without adding extra CYA for a beautiful sparkle all season. This product is great for all pool types and will not fade your pool liner. How To Use HTH Shock Advanced Follow the on pack instructions according to your pool size to add HTH Shock Advanced directly to swimming pool water or skimmer. Make sure to use a clean dry scoop. For best results apply HTH Shock Advanced as part of your weekly pool care routine to keep free available chlorine levels between 1 and 4 ppm. About HTH Pool Care HTH was developed with the pool owner in mind. We know that maintaining your pool water can be a lot of work. That is why we are here every step of the way helping you clear the uncertainty from pool care. With economical easy to use solutions HTH is designed to work hard so you are prepared to tackle whatever life throws in your pool. From balancing your water to treating green water we offer a full line of products to keep your pool water healthy and your swimmers happy.