Swimming Pool Water: Test and Adjust Alkalinity

Three kids at a pool.
  • 1 hours
  • Beginner
  • 15-20

Pool alkalinity is an important factor in keeping your swimming pool water both sanitary and pleasant to swim in. Alkalinity, usually called total alkalinity, measures the water's ability to keep the pH stable, despite use. This ability is called buffering. When the total alkalinity is low, the pH can fluctuate in a seemingly random manner. In actuality, the water is being influenced by everything that comes in contact with it. When the total alkalinity is too high, the pH is essentially fixed in place. This makes corrections to the pH very difficult.

Testing for Total Alkalinity

Total alkalinity is measured in parts per million (ppm). The optimal level is between 80 ppm and 120 ppm. There are two common methods of testing total alkalinity.

In a test strip-style test, take a single strip from the kit and place it in the pool water, at least 18 inches down, for the time noted in the instructions. Remove the strip from the water and hold it for the time specified in the instructions. Compare the color the strip turns to the card provided with your kit to identify the total alkalinity.

The second test style is the basic titration test. This test has three steps listed below. However, always check your test kit's instructions before testing, to ensure you are following the correct procedure.

Step 1 - Add Neutralizer

Add a chlorine neutralizer to the sample water. Without this, the chlorine would give you inaccurate results. Check your kit for the proper number of drops.

Step 2 - Add Test Solution

Add the alkalinity test solution to the sample. Check your kit for the proper number of drops. Swirl to mix.

Step 3 - Add Test Agent

Add the mild acidic test agent, drop by drop, until the sample color changes from green to red. Count the number of drops, multiply by 10, and you have the number of parts per million for your total alkalinity. (Be sure to confirm this ratio with the instructions for your kit.)

Note: If your chlorine levels are too high, the sample may turn blue with the alkalinity test solution and flash to yellow from the acidic test agent. Try doubling the amount of chlorine neutralizer on a fresh sample.

Correcting Low Total Alkalinity

Adding sodium bicarbonate to the water will raise your total alkalinity. You can also use sodium carbonate, also called soda ash, but this will raise your pH at the same time. If you don't need to raise your pH, stick with sodium bicarbonate.

Add sodium bicarbonate at a rate of 1.4 pounds per 10,000 gallons of water in your pool. Let the water circulate for at least an hour before testing again. Repeat if you still have to raise the total alkalinity.

Correcting High Total Alkalinity

Total alkalinity can be lowered with muriatic acid. Add no more than 1 quart of acid per 10,000 gallons of water in your pool at any one treatment. Allow the water to circulate for at least two hours before testing again. Repeat if you still have to lower the total alkalinity.