How To Lower pH In A Pool - Ultimate Guide
One of the most important chemical qualities of pool water is its pH. While low pH levels are associated with acidic water, high pH levels are overly alkaline and can have just as many negative effects for your pool as low pH.
In this article, we will discuss the ideal pH levels in swimming pools and problems associated with high ph. We also talk about testing your pH levels, choosing the right pH decreasing product, and how to reduce pH in pools.
Ideal pH Levels In A Swimming Pool
The range of ideal pH values for a swimming pool is 7.2-7.6, with the sweet spot being at 7.4. This pH level is slightly more alkaline than pure water, mostly due to dissolved compounds or minerals in the pool.
While pH that drops lower than the normal range can become unsafe for swimming due to excess acidity, pH that is too high also has its own detrimental effects.
Problems Associated With High pH
Lower Chlorine Effectiveness
High pH is known for causing many different pool problems. Most notably, it tends to lower the effectiveness of your chlorine (if cyanuric acid levels are low), which can allow bacteria and algae to reproduce at rapid rates within your pool.
This is because hypochlorous acid (the effective form of chlorine) quickly convert into hypochlorite (ineffective chlorine) at high pH levels unless there is adequate cyanuric acid in the water.
High pH is also known to cause cloudy water. This is typically either a side-effect of chlorine inefficiency and therefore a sign of a bacterial or algal bloom, or it can be the result of dissolved calcium forming a solid in the water column.
When the pH of pool water increases, it pushes more of the alkalinity in the water into the carbonate form (CO₃).
If your dissolved calcium (Ca) is also high, the water will eventually reach the point where it cannot hold any more of these dissolved solids, they begin to fall out of suspension as calcium carbonate (CaCO₃), which appears as white or milky, cloudy water.
Eventually, this calcium carbonate will form scaling or calcium deposits on your pool surface. Calcium scale can be unsightly and difficult to remove, but it is an unfortunate consequence of neglected, high pH levels.
Water with a high pH is not technically hazardous to swimmers until levels above 9.0 are reached. However, at any pH level above the normal range, swimmers are likely to notice adverse skin effects.
These effects can include a skin rash or unusual irritation, and will also accelerate problems with dry skin. High pH water that comes in contact with the eyes, nose, or other mucus membranes will also tend to cause much more irritation in these areas than pH balanced water.
How To Test Your pH Levels
In order to test the pH levels of your pool, you will need an appropriate test kit. If you own a testing kit or test strips that test for multiple chemical properties in your pool’s water, then you likely already have a product that is capable of measuring your pool’s pH.
Tech-savvy pool owners may be interested in trying out an electronic pH meter for more precise results, but these gadgets carry a much heftier initial investment price.
Once you have measured the pH levels in your pool, compare them with the appropriate range.
While pH levels that are higher than 7.6 are considered high, only levels that begin to rise above 8.0 necessitate chemical treatment. pH levels that are only slightly high often resolve on their own during rain or other small-volume water changes.
Products That Lower pH
When choosing a product to reduce pH in your pool, you will typically need to decide between hydrochloric acid and sodium bisulphate. While both of these chemicals are highly acidic and should be handled with the utmost care, they tend to vary in form and concentration.
Hydrochloric acid, sometimes referred to as muriatic acid, has an incredibly low pH of around 3.0. At this level, hydrochloric acid is immediately corrosive to the skin and more sensitive areas such as the eyes, nose, and mouth.
Because hydrochloric acid is such a strong acid, only a tiny bit needs to be added to your pool to correct problems with high pH.
The main downside of hydrochloric acid is that it is dangerous to handle and store, especially if you have children in the home. Because this acid is highly corrosive to skin, it can cause permanent chemical burns and related issues.
Inhaling the fumes of hydrochloric acid is also associated with negative health effects, such as a cough, shortness of breath, and development of pneumonia.
Sodium bisulphate is also highly acidic, but unlike hydrochloric acid which comes in the form of a solution, this compound is available as a dry acid or powder.
Dry acids are much safer to use and store than those available in liquid form. Because dry acids only become corrosive when they interact with water, they are more safe in cases of accidental spillage.
Although dry acids like sodium bisulphate are much safer to use than hydrochloric acid, they are also not as potent in terms of acidity. It is likely that much more sodium bisulphate will be required to lower the pH in your pool than hydrochloric acid.
You can use this pool acid dose calculator to work out how much of either chemical is needed to lower your pH.
How To Lower pH In Pool
Gather Your Equipment
To lower the pH of your pool you will need a few basic supplies.
These include your pH decreaser, whether it be sodium bisulphate or hydrochloric acid, as well as a mixing container and stirring stick. You will also need measuring spoons or cups depending on your product choice (don’t use the kitchen ones!).
Although hydrochloric acid can typically be added straight to your pool as the pump is running, dry acids sometimes require mixing. Check the instructions provided on your product’s packaging to determine if you need a non-metallic mixing bucket and stirring rod.
Regardless of the pH decrease you choose to use, you should also use personal safety equipment.
At the bare minimum, it is essential to wear protective eye coverings such as glasses or goggles and to also use gloves in order to prevent accidental contact with these acids.
Calculate The Dosage For Your Pool
In order to calculate the correct dosage of pH decreaser for your pool, you will need to know the volume of your pool in litres as well as your current pH readings. You will also need to know your pool’s current total alkalinity readings.
If you are using a pH decreaser that is composed of sodium bisulphate, dosage instructions should be provided on your product’s packaging. If you cannot locate this information, contact the retailer you purchased your product from.
If you are adjusting the pH of your pool using hydrochloric acid, dosage can be a bit harder to calculate as instructions are not often provided. Luckily, this calculator tool can easily tell you how many millilitres of hydrochloric acid you should add to your pool.
Never add more than 500 ml of hydrochloric acid at one time, regardless of your pH level.
To use the calculator, all you need to do is enter your pool’s volume in litres, your current pH level, your desired pH level, and your pool’s total alkalinity.
You also need to know the concentration of your hydrochloric acid, but if you are unable to locate this information you can use a typical concentration of 30%.
For sodium bisulphate (dry acid), refer to this calculator.
Remember that by lowering pH, you will also lower alkalinity. These calculators will tell you the final alkalinity you can expect after adding the recommended dose of acid.
Add Product To Your Pool
In a well-ventilated area, measure out the correct dosage of your pH lowering product that you previously calculated.
Then, mix the product by adding it into a bucket that is already filled with pool water until any solids are dissolved.
When you are ready to add the product into your pool, distribute the mixture by pouring small amounts out of the bucket around the perimeter of your pool.
Retest Your pH Levels
After leaving your filter and pump running for a few hours, you should then use your testing kit to retest your pH levels. If your levels are still not within the ideal range, use the newly tested levels of your pool to recalculate a second dosage.
High pH levels can cause a number of problems in your pool, ranging from ineffective chlorine, cloudy water, calcium scaling and swimmer discomfort.
Thankfully, lowering the pH level by adding hydrochloric acid or sodium bisulphate (aka dry acid) is a relatively easy task, as long as you wear appropriate safety gear and calculate the necessary dose carefully using one of our calculators.
A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.