pH vs Total Alkalinity – What’s the Difference?
There are some major differences between pH and total alkalinity, but what are they and what do they mean? Let’s take them one at a time.
Technically, pH is one half of an equation as seen below:
pH = -log10(aH+) or alternately pH = log10(1/(aH+))
Doesn’t really help does it? Let’s try it a different way.
pH stands for potential hydrogen or power hydrogen, and it is the measure of the molar concentration of hydrogen ions in a solution. The pH scale goes from 0 to 14 with 7.0 considered neutral. 0 is the acid end of the scale, with pH 0 being hydrochloric acid or battery acid. It will cause severe chemical burns if it gets on your skin or is ingested. On the other end of the scale is bleach at pH 13.5 and liquid drain cleaner at pH 14. Human blood is near the dead center at pH 7.4.
In swimming pool water, problems can arise if the pH of the water gets too high or falls too low. If your pH is too low (acidic) the water could corrode surfaces (especially metal), cause etching on plaster and concrete surfaces, lead to excess chlorine use, and irritate your eyes and skin.
On the other hand, if the pH rises too high, the water becomes more base (or basic) and it could allow scale deposits on pool surfaces, create cloudy water, inhibit the efficiency of the chlorine in the water, and cause eye irritation.
Needless to say, controlling the pH levels in the water is very important for your pool’s maintenance and for protecting swimmers from algae and bacteria.
There are minerals in water that act as what are called “buffering agents”. Total alkalinity is a measurement of those alkaline materials in parts per million (ppm). It measures the capacity of water to neutralize or buffer acids. This capacity is dependent on the amount of carbonate, bicarbonate, hydroxide, borate, silicate, and phosphate.
The recommended range for these minerals in water is 80-120 ppm. If the total alkalinity is too low, your pH levels will drift quite easily (pH bounce), requiring you to make frequent pH adjustments. This in turns means using more of those expensive chemicals. It can also lead to water that is more corrosive.
If the total alkalinity is too high it can keep the pH of your pool water fixed so rigidly in place that it can’t be adjusted without using massive quantities of chemicals, another expense. High alkalinity can also lead to cloudy water, scaling, high pH, and inhibition of chlorine efficiency.
The confusion over pH and total alkalinity arises from the way scientists have defined and used the word alkaline. When pH levels are too high, the water is called base or alkaline. Yet total alkalinity is completely different, a measurement of the amount of mineral buffering agents in the water. This is why you’ll sometimes see it referred to as “Total Alkalinity”, with both words capitalized. If it was simply called alkalinity, there would be a lot of unnecessary confusion over what was meant. There’s enough confusion as it is; we don’t need anymore.
To clarify, pH is about hydrogen concentration. Total Alkalinity is about the ability to buffer or neutralize acids. They’re completely different and when they’re used interchangeably, it creates all sorts of confusion.
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