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How to Balance the Chemicals in a Swimming Pool. What Should the Levels be? Muriatic Acid, Chlorine

Updated on April 8, 2015

Keeping the Balance... The Big Three

There is a lot to pool water chemistry, much more than the average person realizes but most of us know the "Big Three", being Chlorine, pH, and Alkalinity. These three chemicals work hand in hand and MUST be balanced correctly to maintain appearance, comfort and quality of the water. If one of these is out of balance, it can significantly affect the other two so it is always important to be sure these are all adjusted to the right levels.

Chlorine molecule
Chlorine molecule

About Chlorine

The Liquid form of Chlorine that is added to the pool is Sodium Hypochlorite, or bleach. This is usually 10% concentrated whereas household bleach is the same thing except 5% concentrated, so about half the strength.

Calcium Hypochlorite is a granular form of Chlorine usually used to shock the pool.

Lithium Hypochlorite is Chlorine gas and is very, very rarely used. I have only seen one commercial pool that has used this as a sanitizer.

Trichloro-s-triazinetrione or tri-chlor is what the chlorine "pucks" or tablets contain.

When added to the water Chlorine produces hypochlorous acid, hypochlorite ion and hydrogen ion. Hypochlorous acid is the main bacteria killing agent in the water. Together these two are known as "free chlorine" or the available chlorine in the water available for disinfection.

The Chlorine level needs to be between 3.0 to 5.0 ppm or parts per million to maintain a healthy amount of free chlorine.

About pH

pH, or protens hydrogen is what makes the water "comfortable" for instance, people who experience eye discomfort while swimming usually believe the chlorine is too high. This is usually never the case. The human eye has a pH level of 7.5 and so it is important to try to maintain the pool waters pH level as close to this number as possible. A low pH will cause the water to be acidic. This can cause chlorine loss, eye and skin irritation, pool etching, staining, corrosion, etc..High pH can cause filters to clog, cloudy water, eye and skin discomfort. Therefore the recommended pH level is from 7.4 to 7.6.

pH is raised using "pH up" Usually sodium bicarbonate (baking soda) or in some cases, soda ash. It is lowered by adding muriatic acid.

About Alkalinity

Alkalinity measures the ability of the water to resist fluctuations in pH. It is really a buffer to pH. If the alkalinity level is balanced correctly, it is easy to maintain the pH. alkalinity is made up of bicarbonate, carbonate, and hydroxide ions.

Alkalinity level needs to be between 80 and 120 ppm. Ideally 100 ppm.

Testing the Water

I can not stress enough that the test strips that are dipped into the water are simply not accurate. In all states, they are not approved for any commercial aquatic facilities. They give you only a general idea if the pH is high or low, or if the Chlorine is high or low. I highly recommend a higher end test kit, or DPD test kit. This will provide you with an accurate test.

Testing frequency - If you use the pool daily, test daily. If the pool has little use it can be tested once per week and balanced.

Test the Chlorine first. If it is below 3.0ppm, add a half gallon of liquid chlorine, wait an hour before swimming, and make sure there are enough chlorine tablets or sanitizer. If it is high, or above 5.0ppm it will usually come down on its own, but not for a day or two. A chemical known as Sodium Thiosulfate can be added to reduce chlorine immediately.

Now test the pH. If it is low, or below 7.2, add pH up or sodium bicarbonate. The amount will be determined by the size of the pool. An average 15,000 gallon pool with a pH of 7.2 I would normally add about 2 pounds of Sodium Bicarbonate. If the pH is high, or above 8.0, Muriatic acid will be added 8 ounces at a time testing hourly until the desired pH is reached.

Test the alkalinity. If it is low, Sodium Bicarbonate can be added. If you have already adjusted low pH, then naturally the Sodium bicarbonate will raise both the pH and alkalinity. If it is high, muriatic acid can be used to lower it to the desired level.


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  • moronkee profile image

    Moronke Oluwatoyin 4 years ago

    I stopped swimming many years ago. The chlorine in the pool makes my eyes red and I feel the water is not hygienic because I think people urinate in the water.

    However, thanks for the hub. I learnt more about chlorine and pH.