Total Alkalinity Simplified

When teaching seminars and classes on water chemistry and testing, and even during tech calls and e-mails, there have been a lot of questions lately about total alkalinity (TA)—what it is, and its significance in pool/spa water?

I admit the subject can be intimating and a bit confusing. That’s why whenever I talk about TA I like to use a visual — an umbrella!

 

By definition, TA is the buffering capacity of water to resist pH changes. Total alkalinity and pH work together (I like to call pH a little puppy that follows TA everywhere). The same treatment products (acid) that lower pH also lower TA; likewise, the same products (sodium bicarbonate) that raise TA also slightly raise pH. If TA and pH don’t work together, pool/spa water won’t be balanced, leading to a whole slew of problems.

Let’s imagine you have a tiny umbrella (TA). This tiny umbrella is not doing a good job protecting pH from the additional acids or bases in the water from the treatment products. So, pH moves around trying to find its happy place. This is what we refer to as “pH bounce,” which signifies a low TA environment. In other words…the water is underbuffered.

On the other hand, say you have a big beach umbrella hovering over itty-bitty pH. When pH looks ups and sees this gigantic umbrella over it, it gets scared and doesn’t move, creating what we call “pH lock.” Now we have an environment where there is too much TA in the water…the water is overbuffered.

When you have the correct size umbrella (TA) protecting pH, you have the “perfect” scenario.

Here are the current industry recommendations for total alkalinity in pool or spa water:

• Minimum: 60 ppm
• Ideal: 80–120 ppm
• Maximum: 180 ppm

But wait — there’s more!

TA is a tricky little guy, made up of all sorts of components such as carbonates, bicarbonates, hydroxides, and cyanurates (yup, cyanuric acid, our friendly chlorine stabilizer). So, when you’re doing a TA test with a sample that you know for sure has cyanuric acid in it, keep in mind cyanuric acid is adding to the TA level, giving you a “false-high” reading. To get the correct TA value needed for treatment purposes and water balance calculations, you’ll need to know the “carbonate alkalinity” value. Finding this value is actually quite simple: Take 1/3 of your CYA reading and subtract that number from your TA reading.

Example:

CYA test value = 60 ppm; then 1/3 of 60 ppm = 20 ppm (60 ÷ 3 = 20)

TA test value = 100 ppm; then 100 ppm — 20 ppm = 80 ppm (carbonate alkalinity)

Testing for TA is simple and can be done using test strips (for a quick and easy analysis), or with a standard drop test (where a reagent is added drop by drop until the sample color goes from green to red; then the number of drops used to reach that endpoint is multiplied by 10 to get the TA value). There is also a test designed to measure TA using a colorimeter.

Regardless of the method used — test strip, drop test, or colorimeter — a test for TA should be performed at least weekly to make sure your umbrella is on the job!