Swimming Pool Water Testing Basics

New to owning a swimming pool? This article explains water testing and what you need to know to keep your pool water clear and balanced.

It’s great to have a clean and clear pool, but maintaining perfectly balanced pool chemistry can be challenging. It is necessary to learn what each swimming pool water test means and why it’s important in keeping your pool in perfect shape. We will cover the basic components of pool chemistry: free chlorine, pH, total alkalinity and cyanuric acid.

Free Chlorine

Free chlorine is the amount of chlorine available to sanitize the water in your pool. Over time, the ability of the chlorine to sanitize the water will decrease, so adding chlorine (or salt in saltwater pools) is necessary to keep the pool clean.

Free chlorine and total chlorine are often confused. Total chlorine combines the free chlorine AND the chlorine which has already been used to sanitize, and is no longer active.

When you test your swimming pool water, aim for between 1 and 3 ppm (parts per million) of free chlorine. Less than this will not be able to effectively sanitize and more may be harmful to swimmers. When free chlorine levels are low, you can use calcium hypochlorite to increase them.

pH

pH is the measure of the acidity of your pool. It is represented by a scale from 0 to 14. The lower the number, the more acidic your pool water. The higher the number, the more basic your pool water. A seven (7) on the pH scale is considered neutral.

Perfect pool chemistry should keep pH between 7.4 and 7.6, meaning the pool should be slightly more basic than acidic. At this value, the free chlorine in your pool will still be able to disinfect the water and it will not harm swimmers.
You can raise pH levels with borax or soda ash, and you can lower it with sodium bisulfate.

Total Alkalinity

Total alkalinity is the measure of the amount of alkaline substances in your pool. These substances help to neutralize the pH offset of your pool chemistry, hence why pH should be kept above 7.4. These substances also prevent rapid changes in pH.

You should maintain your Total Alkalinity between 80 and 120 ppm. Use Sodium bicarbonate to raise the level of total alkalinity but be mindful while adding! Lowering total alkalinity can be challenging. Be aware if your water looks cloudy after adding sodium bicarbonate.

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Cyanuric Acid

Cyanuric acid is a pool stabilizer and is a big help when adding chlorine to your pool. When you add chlorine, in minutes, the sun can evaporate half of the free chlorine you just added. However, adding cyanuric acid helps stabilize the chlorine molecules. This helps protect them from the UV rays and keeps them active for longer.

Choosing to use cyanuric acid can be a very helpful and cost-effective method of maintaining pool chemistry, though be sure to keep under 100 ppm in your pool. More than this can negate the effectiveness of chlorine to sanitize your pool water.

Read our article about the Relationship between Swimming Pool Chlorine and Cyanuric Acid here.

Test the above values of your pool chemistry often using test strips to ensure the safety and stability of your pool.

Try out our Pool Calculator as you test the values in your pool! For more information on how to care for your pool, see our blogs on Pool Maintenance

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