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Pool Chemistry 101

Beautiful swimming pool in Canada

Operating a swimming pool isn’t nearly as difficult as some people believe as long as you understand the different swimming pool chemicals involved and what job each of them performs. Below we will go over the chemicals used for swimming pools and explain how they work.

Free Chlorine Free chlorine is basically a sanitizer which is used to keep the water clean and safe. However, the chlorine level needs to be replenished constantly to be effective. Chlorine comes in different forms such as in a liquid, via a salt-water chlorine generator, and in bleach. The quickest method of raising the chlorine level is by using the liquid version. Common household bleach also contains chlorine and it can be found in various strengths with 8.25 percent being the most common. In fact, liquid chlorine and bleach is the same thing. However, liquid chlorine is typically stronger at up to 12.5 percent Bleach should be kept in a cool, dark location since it can lose some of its strength after about a month if it’s stored at higher temperatures. The best way to add bleach or liquid chlorine to a pool is to pour it in front of one of the return jets slowly when the pump is operating. You should then keep the pool running for at least an hour to let the chemical circulate through the water. It’s important the free chlorine level is maintained to keep the water properly balanced. You don’t want too little or too much chlorine in the pool. If the chlorine level drops there’s a good chance you’ll get algae in the pool and the water will become unsafe. The best way to check the chlorine level is a simple pool testing kit. It’s a good idea to test the chlorine level every day or two and add chlorine when needed.

PH - Acidity/Alkalinity

The PH - Acidity/Alkalinity in the water needs to be kept between 7.2and 7.8 to properly protect your pool equipment and keep the water irritant-free. If the PH level is too high it can be lowered by adding dry or muriatic acid. Muriatic acid is generally less expensive and works well with a salt-water chlorine generator. Most pool owners without a generator use dry acid because it’s easier to handle. Muriatic acid can also be found in varying strengths. Like free chlorine, add the muriatic acid in front of one of the return jets with the pump running and led it circulate for an hour. As for dry acid, many pool shops sell it under a variety of names such as PH Reducer, PH Down, or PH Decreaser etc. The best way to add it is to dissolve it in a pail of water and then slowly pour it into the pool. You should test the PH level on a regular basis to see if the acidity needs to be raised or lowered. Just remember that anywhere from 7.2 to 8.0 is acceptable and fine for swimming. If the level is under 7.2 you could find the water burns or stings your eyes. When it’s below 6.8 the metal parts of your pool equipment could be damaged and if it’s over 7.8 it can cause calcium scaling. If the PH level needs to be raised it can be done with soda ash or borax. Most pool shops sell soda ash under names such as PH Up and PH Increaser etc.

Total Alkalinity

Total alkalinity helps to keep the PH in proper balance and it also needs to be tested on a regular basis. Too much alkalinity can cause the PH level to rise and you’ll need more chemicals to alter it. A common way to raise the total alkalinity is by spreading baking soda across the water in the pool’s deep end. If the total alkalinity needs to be lowered, make sure the PH is between 7.0 and 7.2 by adding acid to lower it as this will also lower the alkalinity.

Calcium Hardness

Calcium hardness will let you know how much calcium is in the water. Pools with vinyl liners don’t require calcium while plaster pools without salt-water chlorine generators should have a calcium level fm 250 to 350. If the pool has a generator the level should be from 350 to 450. The calcium level can be increased with calcium chloride while the level can be lowered by replacing the water or by reverse osmosis water treatment. The proper level of calcium will help prevent damage to the plaster since high levels can lead to calcium scaling. Many pool shops sell calcium chloride under names such as Hardness Plus and Calcium Hardness Increaser. The best way to add it is to spread it in the pool’s deep end.

Cyanuric Acid

Cyanuric acid is also known as conditioner or stabilizer and it protects the free chlorine from sunlight as well as determining the proper free chlorine level. When the Cyanuric acid level is higher it means you need more fee chlorine. The best level is typically from 30 to 50 if you don’t have a salt-water chlorine generator and from 70 to 80 if you do have a generator. Cyanuric acid is available in both liquid and solid form with the liquid being more expensive. It usually takes about a week for solid stabilizer to show up on your test kit so you won’t need to re-test for it until a week after it’s been added. You can add solid stabilizer by placing it in the skimmer basket and running the pump for 24 hours. However, the stabilizer should be placed in a sock ad after it’s added you shouldn’t clean or backwash the filter for a week. If the acid needs to be lowered, the best way is to replace the water or via reverse osmosis water treatment.


Salt is needed if you have a saltwater chlorine generator and it should be at least 99.4 percent pure. The salt level can be raised with water softener salt crystals or pellets which don’t have any additives and/or rust inhibitors. Pool salt can also be used but is costlier. Just be sure you don’t use deicing salt, rock salt and/or table salt. Feel free to simply pour the salt into the pool and spread it around if possible and run the pump for 24 hours. If you have a saltwater chlorine generator you should turn it off when the salt is added and leave it off for 24 hours.


Borates are considered as an optional way to control the PH level and fight off algae and the recommended level is from 30 to 50 ppm. The level can be increased with muriatic acid and boric or boric acid. For more information on pool chemicals please feel free to contact us at Discount Pool Supply, we offer fast and free shipping across Canada and carry all of the pool checmicals you need to keep your pool crystal clear all season long.

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