TA - Further Reading

What is Total Alkalinity in Pool Water?

Total alkalinity (TA) measures your pool water's ability to resist pH changes. Technically, TA is the sum of all the concentrations of chemical ion species in your pool water that can react with (or consume) a hydrogen ion (H+).

Most of your water’s alkalinity comes from the dissolved inorganic carbon (DIC) in it. DIC is primarily in the form of carbonates - dissolved or aqueous CO2, bicarbonate ion (HCO3-), and carbonate ion (CO32-). However, cyanurates from your stabilizer (cyanuric acid) and borates contribute to your water’s alkalinity. For both carbonate and cyanurate alkalinities, the buffering intensity increases with a decrease in pH, while borate is the opposite, where buffer intensity increases with an increase in pH.

What does Total Alkalinity do in Pool Water?

The most straightforward analogy for TA is this: Water’s TA is a lot like a shock absorber on a car. It keeps the car from bouncing around wildly when you drive. If your water has very low TA, then the pH of the water can jump around wildly like a person attached to a bungee cord.

If the water has too much alkalinity, especially excess carbonate alkalinity (which all pool water has), there will be upward pressure on the pH to constantly rise (the chemical reactions that govern this are explained in more detail in the forum threads).

What is the Relationship Between TA and ph?

TA and pH go hand-in-hand. When TA gets too low (near zero), your pool water’s pH can crash to values lower than 4.5. When TA is too high, the outgassing of dissolved carbon dioxide and subsequent chemical reactions involving the bicarbonate alkalinity will cause hydrogen ions to be consumed, and your pH will rise.

What is the Best Value for TA in Pool Water?

Like pH, there is no “optimal” TA value - your optimal TA value is the value at which your pH is most stable (longest between acid additions). Typically, people find that a TA somewhere between 80-100ppm works well enough.

However, if a pool experiences constant acid demand and the pH rises too quickly, TA can be safely lowered as far as 50 PPM to compensate for this. Despite what the “pool experts” will say, keeping your TA on the low end will not “rot out your equipment” or “destroy your plaster surfaces.”

The TA range in the Recommended Levels Recommended Levels protects your pool surface as long as the pH, TA, and CH can be kept within those ranges.

Why Does the TF-100 state the TA should be between 100-120?

The TA range given in the TF-100 is from Taylor. TFP does not follow that. It is based on using trichlor for chlorination purposes.

TA Can be Negative

The TA test can be zero or negative if a lot of acid is added. When the TA test is immediately red, the TA is zero or negative.

0 TA implies a pH of 4.5, which can rapidly damage a pool and equipment. Either the TA needs to be raised to raise the pH, or the water needs to be drained and replaced ASAP.

To determine the negative TA and how much it needs to be raised, use R-0006 base demand to add drops until the red turns green. Then, multiply the number of drops used by 3.6 to understand how negative the TA is.

You can also use R-0010 Calcium Buffer to titrate, and the multiplier is 33 ppm per drop.

If your TA is zero or negative, add baking soda, 30 ppm TA worth at a time, until your TA tests above 70 ppm. Then, test and adjust your pH.

Why Should TA be Lowered with a SWG?

Usually, a TA on the high end is fine if the pH is stable. However, the TA needs to be adjusted with an SWG. The problem is, INSIDE the cell, the CSI is very different than in bulk pool water.

With high TA and aeration from the bubbles the SWG creates, the pH rise inside the cell will be faster, and there will be more potential for scaling. With the current reversal, the cell tends to stay clean, but the returns will have more calcium snowflakes. Calcium hardness is only one part of the equation.

If the SWG cell pH rises much above 10 (and it can easily do that) and sufficient levels of carbonate ions are available (CO3--), then you will get calcium carbonate precipitation. The higher the TA and pH, the more carbonate anions are available.

Borates are particularly helpful in preventing scale in a SWG because the pKa for boric acid/borate anion buffering is approximately 9. That means you get the maximum buffering capacity at a pH of 9, which tends to hold down the pH rise inside the cell. Keeping the pH below 10 in the SWG cell reduces the risk of calcium and magnesium scaling (insoluble magnesium hydroxide precipitates at a pH of 10.2 or so).

Is TA a Factor in the Pool Waters Calcium Saturation Index?

Like pH, TA is a quantity used to calculate the Calcium Saturation Index (a variant of the Langlier Saturation Index) and, as long as your CSI is within the “balanced” limits, then it does not typically matter what the individual pH or TA values are.

Is TA is affected by CYA levels?

Cyanurate does contribute to the TA.

Some test procedures say you should deduct 1/3 of your CYA from your TA to get an accurate reading, but this produces the carbonate alkalinity value. PoolMath accounts for the effect, and no adjustment is needed for TFP Methods. Taylor, for example, describes the practice of deducting 1/3 of the CYA value, which, in effect, removes the cyanurate alkalinity portion to produce the carbonate alkalinity value. Taylor then uses this carbonate alkalinity value to calculate their Saturation index (SI). In practice, the concentration of the cyanurate ion is pH dependent, whereas, at a pH of 7.0, it is 22% of the CYA. The percentage increases with pH, where at a pH of 8.0, it is 36% of the CYA value.

When cyanuric acid is added to water, the hydrogen ions released lower the TA as much as the resulting cyanurate raises the TA. So, adding cyanuric acid has no net effect on TA.

How is TA Raised in Pool Water?

The simplest way to raise TA is with baking soda (sodium bicarbonate or sodium hydrogen carbonate). If you look at the ingredient in the chemical bottle that pool stores sell as an “alkalinity increaser,” it is precisely that, baking soda!! And, it is often 2X to 3X the price of the stuff in your grocery store.

Chemicals suggested for raising TA. Their effects are:

• Baking Soda = big TA change, small pH change
• Borax = big pH change, small TA change
• Soda Ash/Washing Soda (Sodium Carbonate) = big pH change, big TA change. Probably more TA change than you want. It is never recommended for use.

It is often best to make large TA adjustments in a couple of steps, testing the water after each step. Adding large quantities of baking soda can raise the pH a little, and you don't want the pH to go out of range.

How is TA Lowered in Pool Water?

TA is lowered when you add acid to your water.

If you need to lower your TA level aggressively, see How To Lower Total Alkalinity.

Manufacturers TA recommendation vs TFP

Manufacturers' TA recommendations are often 100-140, while Pool Math says 50-90.

One key difference is that the industry typically suggests using chlorine “pucks,” which are very acidic. In contrast, TFP suggests liquid chlorine or a saltwater generator, both of which tend to see an increase in pH. The industry tends to suggest a higher TA level as this prevents crashing a user's pH level when using pucks, while our lower level TA tends to greatly slow the rate of pH increase, thus using less acid to maintain your pool.

Running a TA below 50

The TA can be very low, with a pH in the 7 to 8 range. For example, if you have distilled water, you can have a pH of 7 with no bicarbonate or carbonate alkalinity. The only alkalinity you will have is enough hydroxide to make the pH 7 vs. 4.5.

At a pH of 7.0, the TA from hydroxide is 0.0000001 moles per liter or about 40 grams in 10,000,000 liters, which is about 0.005 ppm TA.

If you keep the TA very low, calculate the carbonate alkalinity by subtracting the cyanurate and borate alkalinity.

You can use PoolMath to monitor CSI and keep it in a good range. Get PoolMath and keep the CSI in the -0.3 range for the heater and the fiberglass warranty, even though fiberglass and copper should not need CSI.

Low pH puts heaters at risk, so you must be extra careful not to allow the pH to crash, even briefly.

You can go lower than 50, but it requires special attention to several issues that can become problems.

You have less buffer, so you get more movement from added acid. You have to be extra careful not to add too much acid and drop the pH below 7.2.

Pool Store Tests often Report Adjusted Alkalinity

Pool store TA tests often report lower than you get when testing with the TF-100 or Taylor K-2006 TA tests. They subtract about .35 x CYA from the measured TA to get your adjusted TA.

When using TFPC and Pool Math, you do not need to calculate adjusted alkalinity. Input the Total Alkalinity from the TF-100 or K-2006C test into Pool Math, and it will make the necessary adjustments.

The adjusted alkalinity is the TA - (CYA x cf).

cf is the correction factor, which is based on the pH.

pH	CF
7.0	0.22
7.1	0.24
7.2	0.26
7.3	0.28
7.4	0.30
7.5	0.32
7.6	0.33
7.7	0.34
7.8	0.35
7.9	0.36

For example, if the pH = 7.6, TA = 90 and CYA = 70, the adjusted alkalinity is 90 - (70 x 0.33) = 67.

Total alkalinity is the total of ALL chemical species that affect the ability of the water to exchange a proton (H+), which is the measure of pH. Every alkaline species - carbonates, cyanurates, borates, etc.- contributes a certain amount of buffering capacity to the water that depends on the molar contraction of the species and its buffering capacity. So in relation to pH changes, it’s the TA that matters. One only needs to use adjusted alkalinity, which is carbonate alkalinity, when one needs to calculate a saturation index based on calcium carbonate equilibrium (CSI is used in PoolMath). Other than that, there is no other reason to use adjusted alkalinity. As such, TFP calculates adjusted alkalinity in the background so the pool owner doesn’t have to bother with it.