Chlorine is a disinfectant and sanitizer, while shock kills ammonia commonly associated with body oils, saliva, urine and perspiration. The type of shock you use will also account for how much shock you use in the pool. Add shock to the pool water at night when the hot sun is going down. Before you add shock to your pool, you need to know how many gallons of water are in the pool.
Things You'll Need
 Tape measure

Measure the size of the pool to determine how many gallons of water the pool has. Multiply the length by the width by the depth of the pool. Multiply that number by 7.5 if the pool is rectangular or square, and by 5.9 if the pool is round. For pools with a shallow end and a deep end, measure the shallow end, measure the deep end, add the two together and divide by two to find the average depth of the pool. The equation is length times width times depth times 7.5 or 5.9 (multiplier) to derive the number of gallons in the pool.

Use 2 lbs. of lithium hypochlorite for every 10,000 gallons of water in the pool if you have normal use conditions. Use 3 lbs. for every 10,000 gallons if the pool is used heavily. Lithium hypochlorite adds 35 percent available chlorine to the pool and has a pH value of 10.8 parts per million (ppm). Suspend swimming for eight hours after adding the shock.

Use calcium hypochlorite at a rate of 1 lb. per every 10,000 gallons of water in the pool for normal conditions, or use 2 lbs. of product for every 10,000 gallons in pools that are heavily used. Calcium hypochlorite has calcium byproduct that can raise the hardness of the water, but it has about 68 percent available chlorine and a pH of 11.8 ppm. Wait eight hours before swimming in the pool.

Use nonchlorine shock (potassium peroxymonosulfate) at a rate of 1 lb. per every 10,000 gallons of water in the pool for normal conditions, or use 2 lbs. of product for every 10,000 gallons in pools that are heavily used. Nonchlorine potassium peroxymonosulfate has a pH of 2.3 ppm and no available chlorine. You can swim in the pool 15 minutes after adding this product.