Pool Water Chemistry balancing

Recently saw several question posted on line about alkalinity vs pH.  Are they the same? If different how do you control each?
We often use terms which are too similar so they result in confusion. Alkaline is different and measured differently  than Total Alkalinity.  They are sometimes adjusted downward with the same acidic chemicals but the those acids are added differently” If you add acid to pool water rapidly all in one spot it can lower Total Alkalinity while otherwise it will just lower your pH”.
In pool operator’s water chemistry there is a significant difference between alkaline and Total Alkalinity. Of the two terms, Total Alkalinity (TA) is the term more commonly used in pool water chemistry. However, pH is the most significant factor in pool water balance. Pool Water Balance, better described as the pool water’s Saturation Index, (sometimes SI, CSI, or LSI). To avoid confusion pool operators use the term pH to discuss the acidic or alkaline nature of the pool water.

Keeping the pH of pool water 7.0- 7.6 helps your chlorine do it’s job of oxidizing organic matter in the pool and preventing bacteria growth. Actually if Chlorine was our only concern a pH of 6.8 would be even better. However pH below 7.0 over the long term will usually cause other expensive pool and mechanical problems.The two most popular chemicals for lowering pool pH are: muriatic acid or sodium bi-sulfate aka dry acid. For home pools dry acid like this product is preferred as it is somewhat easier to handle than liquid acids. Dry acid is often known by brand names similar to pH minus. The product listed above is a dry acid.

These highly acidic chemicals have different effects on your pool chemistry depending on how they are added. To lower Total Alkalinity (TA) an acid needs to be added rapidly all in one spot preferably in the shallow end. If added by sprinkling the chemical over a large area of the pool surface these same chemicals will lower pH rather than lower Total Alkalinity.

So, Sodium Bi-sulfate can lower the pH of a pool if sprinkled over a larger surface area. If the Sodium Bi-sulfate is added in a concentrated area then it creates a temporary “acid cloud” where the pH is so low that all the total alkalinity of the water within the cloud drops to zero. Within 30 minutes the acid cloud dilutes and the TA of the pool will be lower.

With accurate data and the right calculator (one example) water chemistry math can be pretty simple. Unfortunately, in practice it is even easier to screw up. So especially the 1st few times get some help from somebody versed in pool water chemistry calculations. I know a lot of professional pool operators who do not understand pool water chemistry. Home pool professional staff take classes but they are usually more product sales oriented than math and chemistry problem solving oriented. I recommend the NRPA Aquatic Facility Operator Course. (AFO) Accurate pool/spa data:
Every pool operator needs to keep the following notes on their pool and share these with your pool chemist. Most of these stats do not change very often. So can be checked monthly. However disinfection chemicals can swing your pH widely in less than 24 hours.

1. what is the volume of your pool/spa in gallons.
2. What is the volume of make up water added to you pool per month? (Evaporation +splash out + leaks -rain)
3. what is the TA and Calcium Hardness of your make up water?
4. What is your pool’s:
Total Alkalinity in ppm
Calcium hardness in ppm
Water temperature
5. which chemical form of disinfection are you adding to your pool (Calcium Hypochloride, Sodium Hypoclorite, Tri Chlor, DiChlor etc
6. What is your cyanuric acid level (CyA) aka “chlorine stabilizer” level on your pool. Ideal range is outdoors is 4-15 as by 100 ppm your chlorine will not work at all. Indoor pools do not need any cyanuric acid
7. How many pounds of pool chemical disinfectant are you adding per week?
8. Does your pool water smell like Chloromine or taste like salt?
9. What other chemicals do your regularly add to your pool/spa?

Raising the Total Alkalinity is accomplished with Sodium Bicarbonate (aka Baking Soda).
Raising pH is accomplished with sodium hydroxide (lye) or sodium carbonate (soda ash). Also known by brand names like pH Plus
Raising calcium hardness is accomplished with Calcium Chloride

To be overly technical:
The pH is the measure of a solutions hydrogen-ion concentration. The higher the pH reading, the more alkaline or oxygen rich the fluid is. The lower the pH reading, the more acidic and oxygen deprived the sample is. The pH range is from 0 to 14, with 7.0 being neutral. However, pool test chemicals like phenol red only read accurately from 6.6-7.8 outside of that range the colors do not change so a reading of 6.4 or 8.0 can be extremely misleading.

Total Alkalinity (TA) is the water’s ability to resist pH change. So as TA raises your pH is more stable. At a minimum you would want your pool’s Total alkalinity to be 80 ppm but depending on other factors a TA of 100-250 ppm may also be ideal.

The calculation of the ideal Totally alkalinity is called the “Saturation Index” (SI) and the ideal target range of SI is -0.5 to +0.5 In this range you have “balanced” pool water and you pool and equipment will last decades longer than when the water is out of balance. If the SA is low the water will dissolve concrete and metals in your pool or pumps etc. You’ll see rust stains. If the SA is high the pool water will leave scale on the pool walls and your pool heater. The good news is that while the pool equipment is expensive the chemical supplies to balance your pool water are very cheap in bulk.

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