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How to Balance Your Pool or Spa pH Level

Categories: Chemicals, Q&A Topics, Maintenance & Upkeep
Balancing your swimming pool water could be considered the most important job a pool owner has. Not only can out of balance water corrode surfaces and cause scale deposits, it can be irritating and even dangerous to swimmers. Balancing your water's pH is an important part of maintaining proper water chemistry. In this article we'll cover everything from what pH is to the best chemicals to use to raise and lower the pH.
Just what is pH?
pH or potential of Hydrogen is the measurement of hydrogen in water. The measurement is a scale from 0 to 14 with 7 being neutral. From 0 to 7 water is acidic and from 7 to 14 water is basic. The concept of a sea saw with the fulcrum at 7.0 is a visual example. The correct pH level for your swimming pool or spa is between 7 to 8. A pH of 7.4 to 7.6 is most comfortable to humans.
Now, we can't discuss pH without talking about alkalinity. Alkalinity is water's ability to buffer acid and resist changes in the pH that would make it more acidic. As we stated above, pH measures how acidic or basic a solution is. So pH and alkalinity work together to balance water. What you do to one has an effect on the other. Water that is high in alkalinity has more potential to absorb acid and pH tends to be higher as well. Low alkalinity cannot absorb acid well and pH tends to be lower (in the acidic range). In some situations, you might have high pH with a low Alkalinity and also a low pH with a high Alkalinity. See below for examples.
pH also dictates how well your sanitizer works. On a percentage scale of 0 to 100:
  • pH of 7.0 will allow about 80% of the sanitizer to be active with 20% in reserve.
  • pH of 8.0 your sanitizer is 20% active with 80% in reserve.
A strategy to keep your pH a bit high and adding a few more ppm of sanitizer can yield an acceptable amount of active sanitizer and allow a buffer. Added sanitizer will usually not cause a reaction in swimmers as the pH and alkalinity are more in line with our bodies natural pH balance.
"A" is for alkalinity, it is your first and primary goal to keep your water alkalinity at 100 to 120 ppm in order for you to be able to control your pH. Low alkalinity means a lowered ability to buffer acid. If your alkalinity is below 80 ppm a small dose of anything acidic will cause your pH to drop quickly. High alkalinity will allow you to add acid, which will cause a drop in pH with a slow drop in alkalinity. Once the alkalinity has absorbed the acid, the pH will start to raise. Alas, the sea saw, what you do to one effects the other!
The pH level of your swimming pool should be 7.4. In an ideal setting, an alkalinity of 100 to 120 ppm and a pH of 7.4 is bliss. That creates water that is stable and the pH is relatively easy to control.
Muriatic acid is the product of choice for most applications when you need to drop the alkalinity and tweek the pH. It is available at most hardware stores. Adjusting pH with a high alkalinity using muriatic acid is a calculated, methodical process that usually yields great results with patience.
Sodium bisulfate is a granular or powder acid that should be diluted in water before pouring into the water. This acid is normally used to adjust pH first as it affects alkalinity slowly. If you have a salt water pool, it is not recommended to use this acid as it damages the cell plates.
Sodium bicarbonate (or baking soda) has a pH of 8.4, so you will never overdose the pH beyond that point; but alkalinity will continue to increase with additional bicarbonate. This is the product of choice to balance alkalinity first. It is very forgiving in comparison to soda ash or sodium carbonate.
Sodium carbonate has a pH of 12. This chemical will adjust pH without too much increase in alkalinity. Although caution should be used as a very small dosage will have dramatic effects on your pH resulting in water low in alkalinity and high in pH. This combination creates difficulty in dropping the pH without the alkalinity dropping into the 60s or below resulting in very acidic water. Pool owners who adjust to pH without concern to alkalinity usually end up destroying interior surfaces and heat exchangers, in addition to complaints of itchy skin and burning eyes. The overdose of sodium carbonate results in metals like copper and iron ions that combine into solids and fall out of solution and stain pool interior surfaces. Do not use sodium carbonate to try and raise your alkalinity, it will cause you grief!
There are just three products that I recommend for alkalinity and pH control - muriatic acid and sodium bicarbonate for pools and once in a blue moon, sodium bisulfate for spas.
How To... 
How to lower pH. Muriatic acid or sodium bisufate should be used to get your pH down. You will need to be cognizant of the water's alkalinity. If your alkalinity is too low this could lead to a dramatic drop in pH with just a small dosage.
How to lower alkalinity. The use of muriatic acid will lower alkalinity. When you add muriatic acid to your swimming pool water you will notice the pH drop first and then will begin to rise. You should see a reduction in alkalinity. Muriatic acid is a calculated, methodical process that usually yields great results with patience. Do not overdose the acid trying to get it done in a day.
How to raise alkalinity. The addition of sodium bicarbonate (baking soda) to your swimming pool will increase the alkalinity of the water. The pH will stop at 8.4 which is close to the 7.4 to 7.8 range that you are trying to achieve. If you overdose using sodium bicarbonate you will continue to increase the alkalinity. YES, you can have it go up and over 200 ppm, so pay attention to your dosage.
How to raise pH. If you need to raise the pH in your swimming pool water just a little bit soda ash/ sodium carbonate can be used. Be aware that adding too much sodium carbonate will cause the pH to increase to a point that it may be difficult to bring it down. Adding sodium bicarbonate will raise the pH and also increase the alkalinity. It is much easier to adjust pH with the use of sodium bicarbonate as it will not go over 8.4. If your alkalinity is close to 100 to 120 ppm a small dose of acid will affect the pH without changing the alkalinity.

When it comes to dosages, there is no one dose that applies to all.The size of your pool or spa in terms of gallons and what chemical you are a applying will determine how much of a product is needed. Dollar for dollar I will always recommend a quality test kit or strips like the Taylor K-2005 Test Kit or LaMotte 7-Meter Test Kit, and the Aqua Check Test Strips because they provide charts with dosages. The less expensive three bottle test kits do not provide the accuracy that is required for balancing your water. Purchasing a quality test kit at the beginning of the season is a wise investment. It allows you to test and learn at home rather than drive every week to a pool store.
Lowering high pH with a low alkalinity. Many of you are only concerned about pH. Lowering pH with no concern for alkalinity can result in the alkalinity dropping dangerously low, usually below 80 ppm. Lowering pH by adding acid will continue to lower the alkalinity until you have destroyed the interior finish, liner or heater. Ignore pH until you have an Alkalinity of 100 to 120 ppm, then and only then should you start to address your pH. See raising alkalinity above.
Lowering high alkalinity and high pH. Address the alkalinity by adding acid to lower the pH. The lowered pH will be absorbed by the alkalinity. Once the alkalinity gets into the 100 to 120 ppm range a small dose of acid is all that is needed to adjust the pH. See lowering alkalinity above.
Salt water pools. The chemistry of salt water passing through the cell assembly creates chlorine and sodium hydroxide. Sodium hydroxide has a high pH, lowering pH in a salt water pool is an ongoing task. Be aware that high pH and high alkalinity will cause scale to form in the cell assembly. Lowering your alkalinity to near 100 ppm helps to keep your water stable. It is important to maintain a strategy to watch the alkalinity and try and keep your pH low.
When considering pH and alkalinity a pool owner should be aware of those things that cause them to fluctuate. Your fill water can influence balance as well as what type of sanitizer you are using. Rain and where you are located has a big effect if you get a downpour of several inches in a short duration. Testing your fill water and rain water is always a good practice.
Many sanitizers such as trichlor tablets and granular algae treatments along with dichlor granular sanitizers and shock treatments have stabilizer as an ingredient and can be acidic. Shock treatments and tablets containing calcium hypochlorite contain calcium and can raise the alkalinity and water hardness.
Please note that the examples provided are meant to educate pool owners on the basic concepts of pH and alkalinity water balance. There are other factors that must be considered and they are covered in my article The Eight Components of Balanced Water.
We know this is a lot of information to take in, but don't worry, we are available seven days a week and are just a phone call away if you have any questions about your pool chemistry. 
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