How to Shock Your Swimming Pool
Before you shock your swimming pool, wait until after sunset so the UV rays won't disrupt the process. Then, fill a 5 gallon bucket with water from the pool and slowly pour granular pool shock into the water. Stir up the mixture in the bucket and turn on the pool filter. Next, slowly pour 3/4 of the water into the pool. Refill the bucket with water, stir it to rinse out any residue, and then pour all of the water into the pool.
Shock your pool at least every other week. If you use your pool daily, you should aim for once a week if possible. That will help keep the water sparkling and clean every time you get in. If you only use your pool occasionally, you may be able to get away with monthly treatments, but that's generally not recommended. Add shock after your pool has been heavily used. If you've had a pool party, for instance, you may want to shock your pool that night or the next day. That will help get rid of the excess human waste in the pool, such as skin, oils, and urine. Even if you've just had a few friends over who have used the pool all evening, that may be a good time to shock it afterwards. Watch the weather to shock it after big storms. Big storms with heavy rains can drastically change the chlorine levels in your pool. Therefore, it's a good idea to shock the water after one has passed through. Even if you don't get a big storm, having rain for several days in a row can change your chlorine levels. Similarly, if your pool loses or gains a lot of water for any reason, it's time to shock your pool, such as if you've had a severe drought that's caused the pool to evaporate a lot of water. Put shock in your pool if there's been a bowel-related incident. If a kid or a dog has left some feces in your pool, first clean that out. Then, add shock to the water, which will deal with the bacteria left behind by the feces. If an incident like this one happens at a pool party, it's best to clear the pool. Pick calcium hypochlorite for a cheap, quick fix. This is the cheapest of the pool shocks available. It dissolves quickly, and it's quite strong. However, it also doesn't last as long as most other chemicals, especially in sunlight. Always apply this type at night. This type is usually in granular form, meaning you need to dissolve it before adding it to the pool. Opt for sodium dichlor for a shock that lasts longer. This granular powder dissolves more slowly than calcium hypochlorite, meaning that it will keep working for longer periods in your pool. However, this doesn't contain calcium, thus it won't make your water harder.  Sometimes, you can add this directly to your pool without diluting it. It depends on the brand. Otherwise, dilute it in water. You should also add this one at night. Pick lithium hypochlorite if you have high calcium levels. This product also doesn't have calcium in it, so if you find your calcium levels are high through a test kit, this may be your best option. This product however is the most expensive of all types of chlorine and is becoming hard to find. Choose a non-chlorine product to swim immediately. With most shock mixes, you must wait up to 8 hours to swim in the pool again. However, non-chlorine products are safe to swim in after 15 minutes. Typically, they contain potassium peroxymonosulfate. However, this will not kill algae like products with chlorine will. If you have green algae, choose another product, such as the other ones listed here. Measure the free chlorine in the pool. Dip the test tube from a DPD kit down to a depth of 1.5 feet (0.46 m) to fill it up. Make sure the water reaches the fill line. Place a DPD #1 free chlorine tablet into the water in the tube. With the lid on, shake the tube until the tablet dissolves, then check the color of the water against the chart. You can find these kits online or at pool supply stores; they measure how much chlorine is in the pool. They give the value in parts per million (ppm). Some kits may use drops instead of tablets. Always read the instructions for your kit. Write down the number for the free chlorine in your pool. Check the total chlorine in the pool. Open the test tube. Using the same water already in the tube, add a DPD #3 total chlorine tablet. Put the lid on and shake the tube until the tablet dissolves. Compare the color to the given chart, which will give the total chlorine in ppm. Write down the total chlorine for your pool. Subtract the free chlorine from the total chlorine to find the combined chlorine. Combined chlorines are the result of chlorine mixing with body waste like skin, oil, and urine. When the chlorine mixes like this, it's not as effective at disinfecting the water. Free chlorine is much more effective. For instance, if your total chlorine is 2.5 ppm and your free chlorine is 1.2 ppm, your combined chlorine is 2.5 - 1.2 = 1.3 ppm. Multiply the combined chlorine by 10 to find the breakpoint level. The breakpoint level is when enough free chlorine is in the pool to break down the combined chlorines in your water. If you don't add enough, all the free chlorine will just convert to combined chlorines. If your combined chlorine level was 1.3, multiply that by 10 to equal 13, your breakpoint level. Figure out the desired change amount by subtracting the free chlorine level from the breakpoint level. The desired change amount tells you how much you want the water to change in ppm. That will guide how much chlorine you add to the pool. For instance, the breakpoint level in the example is 13. Subtract the free chlorine level of 1.2 from 13 to get 11.8 ppm, the desired change amount. Divide the volume of your pool by 10,000 gallons. Typically, shock chemicals give an amount it takes to change the ppm level by 1 in 10,000 gallons (38,000 L). Therefore, divide the volume of your pool by 10,000 gallons (38,000 L). For instance, if your pool is 60,000 gallons (230,000 L), divide by 10,000 gallons (38,000 L) to get 6. Always check your product for the correct amount. Multiply the pool volume by the amount of product needed to raise the chlorine level 1 ppm. Check the back of the bottle again. It will tell you how much you need of the product to raise the chlorine level by 1 ppm in 10,000 gallons (38,000 L). For instance, you may need 2 ounces (57 g) of the product to raise the pool by 1 ppm. Multiply that number by the pool volume number you found in the last step and the desired change amount. In the example, that would be 2 ounces (57 g) x 6 x 11.8 ppm = 141.6 ounces (4,010 g). Divide that number by 16 to get pounds: 141.6/16 = 8.85 pounds. Put on safety goggles and gloves and turn your pool on. Also, wear long sleeves and pants that you don't mind messing up. These clothes will help protect you from the chemicals you'll be using. The pool needs to be circulating to mix the shock in. It's best to shock the pool at dusk. This will prevent the sun's UV rays from affecting the chlorine or other chemical and ensures that the majority of the chemical is available to shock the pool. Dissolve the product in a 5 US gal (19 L) if it is granular. Fill the bucket up two-thirds of the way with water. Add 1 pound (0.45 kg) of pool shock to the water, then stir it to mix it in. Go slowly so you don't splash the chemical on yourself. Always be careful with this chemical, as it could burn your skin. Only mix 1 pound (0.45 kg) at a time. If you need more, do it a single bucket at a time. Never put the chemical in first. You risk splashing it out on yourself when you add the water. Pour the shock into the pool slowly, moving around the pool as you do. Whether you're using a liquid product or one you need to mix bucket-by-bucket, add it by walking around your pool and pouring it in at different places. Pour slowly so you don't splash yourself with the chemical. Make sure you don't get it on your skin. If you do, wash it off immediately, then check the back of the bottle to see if they recommend calling poison control. Read the directions on the bottle to see how long to wait before swimming. Usually, you need to wait at least 8 hours to swim, so read the bottle carefully. However, if you're using a non-chlorine shock, you may only need to wait 15 minutes before swimming. Swimming in water with too much chlorine is very dangerous. Wait until the water reads 3 ppm or less when you test it using a DPD kit. 
Shock your pool at least every other week. Add shock after your pool has been heavily used. Watch the weather to shock it after big storms. Put shock in your pool if there's been a bowel-related incident. Pick calcium hypochlorite for a cheap, quick fix. Opt for sodium dichlor for a shock that lasts longer. Pick lithium hypochlorite if you have high calcium levels. Choose a non-chlorine product to swim immediately. Measure the free chlorine in the pool. Check the total chlorine in the pool. Subtract the free chlorine from the total chlorine to find the combined chlorine. Multiply the combined chlorine by 10 to find the breakpoint level. Figure out the desired change amount by subtracting the free chlorine level from the breakpoint level. Divide the volume of your pool by 10,000 gallons. Multiply the pool volume by the amount of product needed to raise the chlorine level 1 ppm. Put on safety goggles and gloves and turn your pool on. Dissolve the product in a 5 US gal (19 L) if it is granular. Pour the shock into the pool slowly, moving around the pool as you do. Read the directions on the bottle to see how long to wait before swimming. 