TA Test Result Question

[DangerBoy]

I have a Taylor test kit. Not sure what number any more as the part of the label where the test kit number is printed is faded and unreadable.

The TA test has three reagents. CR-007, 008 and 009. For every drop of 009 you ad to turn the mixture from green to pink is 10 ppm TA as CaCO3.

When I add the 6th drop the solution goes from green to dark greyish purple. When I add the 7th drop it turns a bright pink or pinky red. I interpret that result to mean my TA is somewhere between 60 and 70 ppm as CaCO3. Is that correct?

I was shooting for a final TA of 60 ppm. Is that result close enough to help maintain a stable pH?

 

[mknauss]

Total Alkalinity

A drop-based test used to measure the alkalinity in water. Alkalinity helps serve as a … Read more…

www.troublefreepool.com

Once the solution turns pink/red and stays, that is your TA level.

It is TA, not just CaCO3 alkalinity. Poolmath handles any calculation changes based on CYA, etc.

 

[Richard320]

When I add the 6th drop the solution goes from green to dark greyish purple. When I add the 7th drop it turns a bright pink or pinky red. I interpret that result to mean my TA is somewhere between 60 and 70 ppm as CaCO3. Is that correct?

I was shooting for a final TA of 60 ppm. Is that result close enough to help maintain a stable pH?

What does the 8th drop do?

For me, I usually see it go green to grey to pale pink to Barbie Pink. Keep going until you hit Barbie Pink and the next drop doesn't make it even brighter. Then deduct that last useless drop. I would say your TA is either 70 or 80, but only you will know.

Either number is acceptable. The exact value is only important to calculate acid doses in poolmath.

 

[DangerBoy]

@mknauss TA is expressed as CaCO3 on water test results. That is the standard way to report Total Alkalinity. The test kit also says right in the instructions that each drop of CR-009 counts as 10 ppm TA as CaCO3.

@Richard320 The solution went to bright barbie pink on the 7th drop. I didn't add an 8th to see if it would get brighter but it definitely wasn't pale pink after the 7th drop.

 

[mknauss]

If you are using a Taylor test kit -- read the following.

TA - Further Reading

www.troublefreepool.com

 

[JamesW]

TA is expressed as CaCO3 on water test results.

Just to clarify a little bit.

TA is reported in units of calcium carbonate "equivalent", but it's not actually all, or even mostly, carbonate.

TA consists of carbonate, bicarbonate, borate, cyanurate, phosphate, sulfate and anything else that can accept a hydrogen ion while the sample is being titrated down to a pH of 4.5.

The difference becomes relevant when calculating the CSI or the amount of carbon dioxide available to offgass and raise the pH.

For CSI, only the carbonate part of the TA is relevant to the CSI.

PoolMath accounts for the constituent species that contribute to the TA when calculating the CSI.

Some other CSI calculators, like the Taylor wheel, don't account for the difference and you have to calculate the "adjusted" TA before using the wheel.

 

[mgtfp]

I was shooting for a final TA of 60 ppm. Is that result close enough to help maintain a stable pH?

See how you go. If pH is stable enough then leave it there. If not, try closer to 50ppm, but don't go below 50ppm. Also important not to have wrong expectations. Even with TA=50ppm, pH will still want to settle somewhere in the higher 7s, low 8s, depending on other parameters like CYA (with higher CYA, you will have less carbonate alkalinity at the same TA reading). So, if for some reason you wanted pH stay stable at 7.2, then that's not going to work (but the rate of pH-rise would still be lower compared to higher TA).

But in any case, it will be much better than following pool shop advice. Some shops do the above mentioned CYA correction, but still call it TA (which it is not anymore - it is then "TA minus CYA-Alkalinity"). There might be a fine-print somewhere mentioning a ("stabilizer correction"). But they still insist on the already high range of 100-150ppm; imagine a "corrected" reading of 150ppm - with CYA=80ppm the actual TA-reading would actually have been nearly 180ppm - a license to print money by selling MA. Always keep that benchmark in mind - following TFP guidelines, you will always be much better off than that, but pH might still not be perfectly stable.

 

[DangerBoy]

TA is reported in units of calcium carbonate "equivalent", but it's not actually all, or even mostly, carbonate.

TA consists of carbonate, bicarbonate, borate, cyanurate, phosphate, sulfate and anything else that can accept a hydrogen ion while the sample is being titrated down to a pH of 4.5.

Interesting! I didn't know that the concentrations of borate, cyanurate, phosphate, sulfate and anything else that can accept a hydrogen ion while the sample is being titrated down to a pH of 4.5 were reflected in the TA result. I thought it was just carbonate and bicarbonate carbonate concentrations that TA represented. With respect to the water here, it's pretty much all bicarbonate as carbonate concentrations are small in comparison to bicarb at ambient pH levels. The water in my tub at startup TA adjustment time would have no borate or cyanurate and the concentrations of phosphate and sulfate would be low as well.

Our rivers come from limestone mountains just to the west of us and pass over a lot of (Devonian) limestone along the way. The water also contacts a lot of younger (Cretaceous) sandstone but silicates like sandstone are highly insoluble so contribute little to the anion chemistry of our river water. Cations are another story. The water does not come into contact with many evaporite minerals like gypsum or epson salt (Ca and Mg sulphate, respectively) so sulphate levels in our river water are also quite low. The river water I was dealing with can be characterized as a Ca - Mg Bicarbonate water with a Ca hardness level in the 200s and TA in the low to mid 100s. As such, when I treat that water to drop TA down to 60, I'm mainly lowering the bicarbonate concentration.

Thanks for that information though. I learned something new today that will actually help me with my work.