Shocking your water involves raising the chlorine to a level that is significantly higher than you would normally maintain. These increased levels of chlorine will kill large amounts of algae or other unwanted gunk much more quickly than regular levels.
Frankly, there is no specific reason to shock your water unless you develop a problem. The purpose of shocking your water is to overpower a large outbreak of algae that has already established itself. If you keep your chlorine & stabilizer at their reccomended levels, algae and other unwanted gunk will never have an opportunity to get established. With that said, if you have a high swimmer load on certain days, it may be a good idea to go ahead and shock just to make sure that your water stays sanitary and sparkling clean. But, this does not need to be a weekly or even monthly routine. Shocking should be seen as an “as needed” treatment.
Many Intex pool owners will buy bottles of “shock treatment” or “algaecide” from stores. There is nothing especially wrong with this, however you can get the same effectiveness by simply adding more chlorine to your water (adding liquid bleach, or programming your salt water chlorine generator to stay on for longer).
Remember that your normal chlorine level is related to the amount of stabilizer in your water and should be maintained between 10% and 15% of your stabilizer level. The level of chlorine to shock your pool is also related to your stabilizer level. Generally speaking a good shock level is about 40% of your stabilizer level. To get this value, multiply your stabilizer level by 0.4. So if your stabilizer is at 40, you’ll need to raise your chlorine level to 16 to shock your pool. If your stabilizer is at 70, you’ll need to raise your chlorine to 28 to shock. As always, use the calculator at www.poolcalculator.com to know how much bleach to add to reach your shock level.
Finally, in order for your shock to be effective, you can’t just add one dose of chlorine. Instead, you need to maintain those high levels of chlorine for a length of time. If you are doing a shock after a high swimmer load, 12-15 hours should be sufficient. If you are recovering from a bad algae outbreak, you will want to maintain the high levels for 24-36 hours after your water has cleared up. Measure your chlorine levels every 3-5 hours and if it’s dropped below shock level, then calculate & add more chlorine. The more often you maintain these levels, the sooner your water will clear up.