pH vs. Total Alkalinity

I once had a customer ask me what the difference was between pH and Total Alkalinity.  She was convinced they were the same thing, and that it was just a way for pool companies to make more money.  First of all, I assure you this is not the case.  To understand the importance of both of these components, let’s first look at pH (potential Hydrogen).  The pH scale runs from 0-14 with 7.0 being neutral.  A pH of 0-6.9 is acidic (more acidic as you get closer to 0), and a pH of 7.1-14 is basic (more basic as you get closer to 14).  When looking at pool water, you want the pH to be slightly basic with the ideal range being 7.2-7.6.  Problems can arise if your pool’s pH falls too low or gets too high.  If your pH becomes too low, and therefore is acidic, the water could potentially:

–          corrode surfaces and equipment (especially metal!)

–          etches plaster and concrete surfaces

–          lead to excess sanitizer use (chlorine burns off much faster!)

–          irritate bather’s skin and eyes

If your pH becomes too high, and therefore is more basic, the water could potentially:

–          allow scale deposits on surfaces and equipment

–          become cloudy

–          lead to poor sanitizer efficiency

–          cause eye irritation

Obviously, keeping your pH where it should be is very important for pool maintenance and swimmer safety.

Now let’s look at Total Alkalinity.  There are minerals in your pool’s water that act as buffering agents.  Total Alkalinity is the measurement of these alkaline materials the help prevent changes in pH (which we now know is bad).  The recommended range is 80-120ppm.  If your Total Alkalinity is low, the pH will easily drift making frequent pH adjustments necessary (therefore more chemical costs) and will allow the water to have more corrosive tendencies.  If the Total Alkalinity is too high, there are other potential issues that can arise.  High alkalinity can keep the water’s pH rigidly fixed so that it cannot be easily adjusted when needed.  If pH adjustments are necessary, you will need to use an unusually large amount of treatment chemical to correct the pH.  With high alkalinity, you can also potentially have issues with cloudy water, scaling on pool components, and high pH and low sanitizer efficiency (since sanitizer…aka chlorine for most…is pH dependent).

So, like I said before, pH and Total Alkalinity are both very important components of your water chemistry.  While yes they are related, they both have different jobs that are crucial in maintaining a healthy pool.  With regular pool water testing, you can easily keep these levels in check and prevent many potential problems.


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10 Responses to pH vs. Total Alkalinity

  1. Greg says:

    Congratulations on a great explanation, even I get it !

  2. karuna shanker pandey says:

    clear reason why m alkalinity is total alkalinity

  3. Lori says:

    Thank you so much for explaining all of that in plain English for someone who knows absolutely nothing about chemistry. I also wondered if ph and alkalinity were basically the same thing!

  4. Ron Cote says:

    Thanks very much for a very clear explanation. Other sites talked about the tendency to prevent pH change but your explanation took it from the abstract to the concrete. (No pun.)
    “There are minerals in your pool’s water that act as buffering agents. Total Alkalinity is the measurement of these alkaline materials the help prevent changes in pH …”. Just perfect! THANK YOU! 🙂

  5. Tom says:

    This makes sense as long as we understand that when we measure alkalinity we are measuring something other than how alkaline the water is. Because high pH is the definition of alkaline.

  6. Gordon says:

    Very helpful thankyou, here is another post that I found helpful.

  7. AM says:

    If my PH is way high (7.8) couldn’t I just dump some water and refill with fresh water?

  8. Rick says:

    Thank you. First good explanation I have read.

  9. Mary says:

    Help my ph is not high and alkalinity is way high. Super soft well water with zero cya on the test. I keep chlorine fine at 1 or just above. Help. Green pool. New owner

  10. John Knorr says:

    Great explanation! I was confused bc my last test was telling me to add bicarb bc the alkalinity was low (70ppm) and dry acid bc my pH was high (7.8)… I thought it seemed counter-intuitive.

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