You’ve just tested the pool water with your test kit or strips and it’s indicating a high pH above 7.8.
You need to lower the pool pH to ensure your pool water is balanced and correctly sanitized.
How to lower pH in a swimming pool is one of the most common issues that pool owners encounter so let’s find out the answer.
Your pool water is now more alkaline than normal. The water has to become more acidic and the simplest way to do that is by adding acid to the pool until the pH becomes lower than 7.8. For safety reasons and ease of handling, it’s recommended to use a dry, granular form of acid such as sodium bisulphate.
Table of Contents
What is pH?
pH is a scale in chemistry to indicate the level of acidity or alkalinity of an aqueous (water-based) solution. The symbol pH means “power or potential of hydrogen”.
The pH scale is an inverse logarithmic scale indicating the concentration of hydrogen ions in solution. The lower the pH the higher the concentration of hydrogen ions and the more acid the solution. The higher the pH the lower the concentration of hydrogen ions and the more alkaline the solution.
Strong acid is pH 0, Strong base (or alkaline) is pH 14.
Pure water, at 25C, is neutral at pH 7.
Sea water is normally between pH 7.5 and 8.4.
Swimming pool water should normally be between pH 7.2 and 7.8 which is slightly alkaline and never acidic.
Why Balance pH?
It is crucial to have properly balanced pool water at the correct pH. This ensures that other chemicals, such as chlorine, are effective in keeping your pool clean and sanitized.
When pH is too high (alkaline) you will get calcium scaling forming on the sides and the water may turn cloudy.
When the pH is too low (acidic) the water may corrode pool equipment, cause etching in the pool surfaces and irritate your eyes and skin. After all, you don’t want to be swimming in a mild acid bath!
At the correct pH your pool water will feel soft and gentle on your body. There will be no irritation to your eyes because the pH of the tears in your eyes are the same as the pH of the pool water.
How to Measure pH in a Swimming Pool?
Every pool owner must have a test kit or chemical test strips to regularly check the basic primary chemical indicators that show the health of your pool water. These are pH, total alkalinity, free chlorine and stabilizer (cyanuric acid).
If you have a salt water pool you will need a separate test for salinity.
When to Measure pH in a Swimming Pool
The best time to test your pool water is when the pump has just finished filtering, chlorinating and circulating the pool water for the day. Some pool owners like to run their pumps twice or three times a day to more fully circulate the water and mix in any added chemicals. In summer, it’s a good idea to run the pump early for a few hours to prepare the pool for the day and run it again in the evening to clean the pool after use.
If this is the case, just test the water after one of the pump cycles.
Make sure you test water from elbow depth and not just from the surface. Lower a plastic cup upside down (keeping the inside full of air) into the pool up to your elbow. Turn the cup over and fill with water and take out of the pool. Some recommend to take a sample from the deep end and another sample from the shallow end away from the skimmer box. Use this water to fill your test kit vials or simply dip your test strip in the cup of water. Follow the instructions on your test kit.
Check the color of the water in the vial or color on the test strip to the standard provided on the kit to check the pH.
How to Lower pH in a Swimming Pool
The two common chemicals used to lower pH in swimming pool water are sodium bisulphate and muriatic acid.
Sodium bisulphate is a dry acid packaged in a granular form which makes handling and storage easy.
Muriatic acid, which is a form of hydrochloric acid (HCl), comes in liquid form and is more dangerous for handling and storage. This acid can be used to perform an acid wash of pool surfaces to clean away algae, scale and calcium build up.
There are many commercially available products with brand names such as “pH Down”, “pH Reducer”, “pH Minus”, etc. All of these products are suitable to reduce the level of pH in a pool. Some are suited to salt water, some fresh water or hot tubs. Mostly they are a form of sodium bisulphate. Choose the right one for your pool and always ensure your read the instructions on the label of the container to use the correct dosage.
To add the chemical, turn on the pump, pour the chemical into the water where the outlet jets return water to the pool. This will help mix the acid into the water and circulate it around the whole pool. Now run the pump for at least 15 minutes.
If you have an above-ground pool, you will need to mix small amounts of chemical into a bucket of water and manually spread it around the pool.
Common Mistake when Lowering pH in a Pool
One of the most common mistakes pool owners make is adding to much chemical, not mixing it thoroughly and not testing the water again. This leads to over-correction and having to purchase another chemical to bring the water back the other way. I recommend adding 80% of the dosage indicated on the container label to ensure you are not over-dosing the pool. If that is not enough you can always add a little more chemical later.
Remember, it’s important to wear gloves, eye protection and clothing when handling pool chemicals. Don’t add powdered pool chemicals when it’s windy as it will blow everywhere.
Lower pH in a Saltwater Pool
Lowering pH in a saltwater pool is the same procedure as a fresh water pool except that the pool water contains salt. This may slightly change the way the water responds to adding chemicals.
Salt water will require a different dosage per 1000 gallons of water than a fresh water pool. Please read the instructions on your product label to ensure you are using the correct dosage for your type of pool.
Lower pH in a Pool Naturally
If the pH in your pool is only a little bit high there is one method to naturally reduce the alkalinity of the water without adding chemicals.
Wait for a weather forecast of rain. You can drain some water out and let the rainfall fill up the pool again. As rain is usually slightly acidic this will help to lower the pH of your pool water.
You only need to drain water to the lower level of the skimmer box flap by turning the valve at the pump to the drain and running the pump for a few minutes. You still want the pump and filter to operate normally with sufficient water flow so don’t drain too much water. When it rains the pool water will slowly rise and the pH will slightly fall as the pump mixes in the rainwater. Your chlorinator will automatically generate new chlorine to maintain an adequate free chlorine level in the water.
Another method is to use tap water.
Is your town water supply pH neutral? You could drain some water from your pool and top up with tap water to reduce the pH.
Keeping pH Levels Balanced
You have now successfully adjusted the pH of your pool water but how do you ensure it stays in the normal pH range?
Usually when the water is correctly balanced and your filtration system is running effectively the water pH should be stable.
If the pool water pH does fluctuate unexpectedly check the total alkalinity of the water as a high reading will cause pH the change rapidly.
Heavy rain can lower pH as the rainfall is slightly acid so always check your pool after a storm. Or install a pool cover to prevent rainwater entering the pool.
Read our article on How to Raise the pH Level in Pool Water
Safety and Handling
Pool chemicals are dangerous and reactive.
Please ensure that all pool chemicals are stored in a cool, dry location.
Please ensure the chemicals are kept out of the reach of children.
Always wear gloves and protective clothing when handling chemicals.
Always carefully read the instructions on the packaging.
NEVER MIX CHEMICALS TOGETHER
You should never mix pool chemicals together. They may react leading to fire, explosion or release of toxic chlorine gas. Even mixing dry chlorine with liquid chlorine may cause an explosion.
NEVER ADD WATER TO CHEMICALS, ALWAYS ADD CHEMICALS TO WATER.
You must never add water to chemicals. The chemical may react with the water causing an explosion or the release of toxic chlorine gas that has the potential to damage your lungs.
Conclusion
Your pool pH must be within the specified range otherwise your pool chemistry will be out of balance.
Once you have attained the correct pH level for your pool follow your normal pool maintenance routine. You should have trouble-free enjoyment of your sparkling pool. Your pool will look great and the water will be clean, clear and inviting.
