Water Chemistry Guide

Water chemistry is the most important part of owning and maintaining a pool. Proper water balance not only ensures that your pool water is clean and safe to swim in, the right balance of chemicals also extends the life of your pool and pool equipment. There are some basic chemicals that every pool owner should be familiar with and test for on a regular basis. It is recommended to test your pool water at least once a week using either test strips or a liquid test for the following chemical levels.

Free Chlorine

Free chlorine is the sanitizer that keeps your pool clean and germ free. If you allow your Free Chlorine level to fall too low you run the risk of algae growth. A good balance level of free chlorine is between 2 and 5 parts per million (ppm). Free chlorine can either leave your pool by being broken down by the sun or dissolving organic material in the pool. Chlorine needs to be added to the pool daily, either by using a daily quick dissolving chlorine tablet or powder directly into the pool, or a slow dissolving tablet in a chlorinator about once a week. Be sure to check your Free Chlorine level frequently to keep your pool clean and germ free.

Combined Chlorine

Combined Chlorine is the level of chlorine that is in the process of breaking down material in your pool. An ideal level of Combined Chlorine is between 0 and .5 ppm. If your Combined Chlorine level is higher than a .5 ppm reading then it is necessary to shock your pool. Proper control of Free Chlorine will limit the amount of Combined Chlorine in the pool.


The PH level in your pool tells you how acidic or basic the pool water is. The higher the PH the more basic it is and the lower the PH the more acidic it is. A good PH range is from 7.2 to 7.8 while 7.5 to 7.8 is ideal. PH levels that are too low can cause eye irritation (often mistaken for poor chlorine levels) and even damage to pool filters and equipment. PH that is too high can cause scaling of the pool. Also, your other pool chemicals work best in a PH balanced pool. PH increase is used to raise your PH and PH decrease is used to lower PH levels.

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Total Alkalinity

Total Alkalinity acts as a stabilizer for your PH level. Unbalanced Total Alkalinity can cause your pool's PH level to bounce around out of control. A good Total Alkalinity range is from 80 ppm to 120 ppm. Total Alkalinity Increaser is the best way to raise your Total Alkalinity level. Alkalinity is best adjusted in small steps since this chemical can also raise your PH slightly. Adding a few lbs at a time and retesting after a few hours will help prevent you from raising your PH out of range.

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Chlorine Stabilizer

Chlorine Stabilizer, also referred to as cyanuric acid acts as a sunscreen for your Free Chlorine. The higher your Stabilizer level, the slower your Free Chlorine breaks down from the sun. An ideal range of Chlorine Stabilizer is between 30 and 50 ppm. As you go higher than 50 ppm cyanuric acid will start to diminish the sanitizing properties of your chlorine. It is best to add this chemical slowly through the skimmer and allow 2 to 3 days before retesting since this chemical dissolves slowly. Retesting and adding more too fast can result in a high Stabilizer level. There is no easy way to decrease this reading other than diluting the water with new water.

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Calcium Hardness

Calcium Hardness controls how hard or soft your water is. Depending on the surface of your pool (vinyl, concrete, plaster, gunite, etc.) ideal ranges can fluctuate. Water lacking in calcium can start to absorb the calcium in the walls of concrete and plaster pools. Water with low or high calcium levels can also damage your filter and other pool equipment. Vinyl pools require a Hardness level between 100 and 150 ppm, while a plaster or concrete pool should see a Hardness level between 250 and 350.

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