Cyanuric Acid and Alkalinity.

[Freelancer]

Cyanuric Acid and Alkalinity.

I'm not sure if this has been posted elsewhere and I've read quite a few posts but not seen it mentioned.

I read a paper some time ago regarding the Total Alkalinity and Cyanuric Acid.

It stated you must use a correction factor to correctly ascertain your correct alkalinity level when taking an Alkalinity reading. When doing so the PH must be between 7.2 and 7.8.

The formulae used was..

TA - 1/3 CYA = Actual TA eg TA= 80 PPM - CYA= 75 PPM/3 80 - 25 = 55 PPM..

So if you got a reading of 80 for your ALK you would think that it was OK but according to this paper the actual reading (55 PPM) is too low and requires attention.

The reason given was that the alkalinity component of the CSI is based solely upon carbonate alkalinity and TA testing cannot distinguish cyanurates from carbonates and bicarbonates all of which make up the Alkalinity reading.

Does anybody have any thoughts on this because if your test kit measure Total Alkalinity and this statement is true then it might be something worth knowing.

The article was published in Aquatics International.

 

[spishex]

You can factor in the pH at lower and higher ranges, too. The correction factor is used for calculating the Langelier Saturation Index which we don't use. The factor is also pretty small (if your CYA is in line) so it's usually below the margin of error of the test to begin with.

Here's a thread about it.

 

[JasonLion]

The short answer is that the correction factor allow you to estimate the carbonate alkalinity. However, the total alkalinity is the number that influences how the PH changes, which is what matters to swimming pools. It doesn't make any difference what portion of that is due to carbonate (unless you are calculating the LSI).

 

[chem geek]

When the paper says the adjusted TA is too low and requires attention, they are saying that with respect to the saturation index. As noted, you only need to adjust the TA when calculating the saturation index and that is done automatically for you when you use The Pool Calculator so you don't need to worry about it. You generally set your TA at a level where the pH is relatively stable and then adjust other parameters, including Calcium Hardness (CH), to get the saturation index near zero. If a pool is experiencing a rise in pH over time, then lowering the TA level usually helps reduce that rate of rise if the rise is due to carbon dioxide outgassing (as opposed to plaster curing, for example).

 

[Freelancer]

Thanks very much for your answers guys..

So just to clarify then the TA reading if it says 90 then that is good enough for your pool and no need to use a CYA correction..

 

[chem geek]

Yes. If you find your pH to be relatively stable and you aren't adding acid frequently to maintain pH, then you're good to go with a TA of 90. You can put in the other water parameters into The Pool Calculator to calculate the calcite saturation index and can adjust if needed.

 

[Jaywalker]

In this particular version of the CYA/TA issue (James Brennan's evaluation of John A. Wojtowicz's work), the attached paper at the link (the "Correct Approach") does say the TA test cannot distinguish between cyanurates (presumably 30% of the total) and carbonates/bicarbonates.

I understand the discussion in our forum above indicates the Pool Calculator adjusts in certain fields, but I'm missing the adjusted field that tells me whether to drop my TA level in the first place. In my case (CYA 100) my TA test indicated 140, so I followed the calculator guidance to lower it to 120, its now current reading. Did I really need to add acid? Did I really have a 140 TA or was it actually 70% of that figure, 98? Is my current TA 120, or is it really 84?

http://www.tricitypool.com/tc-cyanuric.html - pathway to Brennan's paper.

Thanks.

 

[JasonLion]

TA is total alkalinity, the higher number, the sum of all kinds of alkalinity, is the one measured by the test kit. TA is the number that we always use around here, the one used in our recommended levels. This is the only number you normally need to think about, since it is the one that predicts how the PH is going to change in response to chemical additions, which is the main reason you might have for adjusting TA.

The lower number is ATA, adjusted total alkalinity, gotten by subtracting the alkalinity due to CYA from TA, is nominally the carbonate alkalinity (it might include alkalinity from other sources, but is normally going to be almost all carbonate alkalinity). This number is only useful if you are calculating LSI (a calcium saturation index). We never use it here, and it isn't something you need to worry about. If you are using The Pool Calculator you should enter the numbers directly from the test kit and it will do all of the adjusting for you.

Did you need to lower the TA? Probably not, though it doesn't hurt. Having TA a little higher than ideal is not normally a problem. High TA can become a problem if you have a source of aeration (SWG, fountain, waterfall, etc) or have problems with rapidly rising PH.

 

[Jaywalker]

Thanks, Jason. Not to put too fine a point on it, but you're saying that pH buffering ability varies with TA, not ATA? I did find a reference, since lost, that claimed cyanurates added no pH buffering and should therefore be disregarded for that purpose.

 

[JasonLion]

Yes, CYA will buffer the PH. There are some technical differences in the details of how CYA buffers PH vs how carbonate alkalinity buffers PH, but they are not particularly important to know about.

 

[chem geek]

This post in The Deep End shows the different pH buffering effects from different levels of TA, CYA and Borates. The claim that cyanurates do not affect pH buffering is just plain wrong. CYA does not affect the calcite saturation index (perhaps that is what they meant?) and is why the adjusted TA is used for that calculation (or is derived from TA, CYA and Borates entries, which is what The Pool Calculator does).