As a kid, I always wanted to live in a house with a pool, but I grew up in the middle of nowhere, where ponds were much more likely to be; you know, the kind with tons of algae, sandy bottoms, and murky water. While I don’t yet live in a house with a pool (I live in an apartment in Manhattan), my brother who lives nearby has a pool and a house. He’s also the head of a university’s chemistry department, which comes in handy when doing pool maintenance (who knew pools involved so much chemistry). I have learned that pool owners spend a lot of time balancing pH and alkaline levels.
A high pH in a pool can cause a great deal of discomfort; including cloudy water and algae growth like my childhood ponds, as well as itchy eyes and skin and damage to pool parts.
PH refers to the “potential of hydrogen” of an aqueous solution; in this case: your pool. It measures the acidity of a substance on a scale of 0 to 14. Anything below 7 is considered acidic, while anything above 7 is called “basic.” Chemistry defines a ‘base’ as any aqueous solution of a chemical compound that has a lower concentration of hydrogen than is found in pure water, such as ammonia. They contain ions, can conduct electricity, and feel slippery. Soapy water is an example. Bases and acids are chemical opposites.
To lower the pH in a pool, you need to add more acid. The three acids used as pH reducers include sodium bisulfate (dry acid), muriatic acid, and sulfuric acid.
Both sodium bisulfate and sulfuric acid add sulfates (indicated by their names) to your water that could cause other problems like corrosion of metal parts, degradation of a saltwater generator (if you have one), or damage to concrete . For these reasons, some experts recommend using muriatic acid over the other two.
How to lower the pH of your pool
taste the water
This test kit contains 100 strips that measure your pool’s Hardness, Chlorine, Bromine, Free Chlorine, pH, Cyanuric Acid and Alkalinity. Simply dip a strip into your pool, remove it and carefully shake off excess water, then compare the colors to the chart on the side of the container.
Test your water for both alkalinity and pH levels. The total alkalinity of your pool affects the pH level, which helps keep it balanced, kind of like a good friend. If alkalinity needs to be adjusted, do so first and then address the pH level.
In general, the alkalinity should be between 80 and 120 parts per million (ppm) and the pH should be between 7.4 and 7.8. If the alkalinity is lower than it should be but your pH is high, increase the alkalinity first by using baking soda (baking soda). Adding 680 grams (or 1.5 pounds) of baking soda per 10,000 gallons of water will increase the total alkalinity by 10 ppm without having much effect on the pH level. Products like Alkalinity Up and Alkalinity Increaser are essentially just baking soda with a fancier name.
Here are some quick calculations of average alkalinity per 10,000 gallons, courtesy of my brother. Products made specifically for pool care will have dosage charts printed on the package.
- 5 ounces of baking soda will increase total alkalinity by 2 ppm
- 14 oz of baking soda will increase total alkalinity by 5 ppm
- 27 oz of baking soda will increase total alkalinity by 10 ppm
On the other hand, if the alkalinity is too high, you can lower it as much as the pH by using sodium bisulfate or another pH reducer.
Calculate the volume of your pool
Calculate the volume of your pool in gallons so you know how much acid you need to add.
For rectangular pools use: length x width x depth x 7.5 = volume in gallons
For round and oval use: diameter x diameter x 5.9 = volume in gallons
measure additive
Muriatic acid
sodium bisulfate
EcoClean Solutions
amazon.com
$52.98
Sulfuric acid
Taylor Technologies
amazon.com
$35.99
Be sure to wear safety glasses and chemical resistant gloves and long sleeves and pants when working with any of these acids. After all, they are acidic and you don’t want them in their concentrated state on your skin or in your eyes. Muriatic acid, or hydrochloric acid, in particular is very dangerous. Cover your body completely and wear a mask. Do not use it on a windy day.
First dissolve the acid in a 5 gallon bucket of clean water if using a dry acid (or baking soda to increase alkalinity).
Be sure to read the package directions to determine how much acid to add.
Some general measurements for 10,000 gallons are:
- 10 oz of 15% muriatic acid will lower the pH by 0.1
- 5 oz of 31% muriatic acid will lower the pH by 0.1
- 7 oz of dry acid will lower the pH by 0.1
Pour the solution into your pool
Pour dissolved acid solution or liquid acid if using muriatic or sulfuric acid onto pool decks with pump running. Allow the solution to settle and your pump to do its job for fifteen to thirty minutes, then test the water again. Repeat the process if necessary.
Once the pH level is where it should be, check the alkalinity. If your alkalinity has dropped too low, use baking soda (as described above) to bring it up again.
Causes of too high a pH in a pool
Rain, dirt, algae, and debris can affect the pH level, so try to clean your pool weekly and be sure to test your water at least once a month. Water features will raise the pH level because movement speeds up the aeration or “outgassing” of carbon dioxide. As CO2 leaves the water, the pH level increases. Saltwater generators or chlorinators also create bubbles by converting salt to chlorine, which results in aeration.
If you re-plaster your pool, that can cause a high pH level. New plaster releases calcium hydroxide for up to 30 days, which has a pH level of 12 by itself.
Achieving the correct balance of chemicals in your pool water is not difficult, as long as you stay on top of cleaning and testing. Sometimes when I visit my brother, we sit in his backyard near the pool while his children swim and reminisce about our childhood and the farm ponds we grew up in. So we weren’t afraid, we’d wade into our grandmother’s pond through a willow branch, sink our toes into the soft, muddy bottom, and have what we called algae fights. I’m glad I had those experiences, but I’m also equally glad to swim in a well-maintained, chemically balanced pool. It’s about achieving balance, after all.
