As debris builds up in the water (such as perspiration, urine, suntan oil, and hair spray), it can cause eye and skin irritation and dull water. These contaminants tie up chlorine, keeping it from effectively sanitizing the water. When this occurs, it is time to add shock to your pool. Pool shock, available in either chlorine or non-chlorine formulas, oxidizes contaminants and frees up the chlorine to keep your pool crystal clear. Weekly pool shock treatments will also kill resistant algae in the water. To prevent algae from forming in the first place, include a weekly treatment of algaecide.