High FC and TA

[yann]

Hi all

I know PH is affected by FC levels above 10ppm

How about TA? Does FC have to be <10ppm for accurate testing?

Thanks

 

[AUSpool]

No. The first reagent added neutralises the FC. If you suspect high FC you can add an extra drop of the first reagent, for Taylor reagents its the r-0007, for CCL its the buffer, reagent 2? Reagent 1 is the reaction cylinder?

Trouble Free Pool

I need to ask though, are you asking about FC affecting the test results or the actual level in the pool?

 

[yann]

My FC is 12pm, coming down from recent SLAM so I'm not concerned there.
I am due to a full test this weekend so I wanted to know if I could test my TA accurately in case my FC still above 10ppm
I know CH and CYA aren't affected but I was wondering if TA would be.
Yes with CCL kits #1 is the test tube. I guess they call it #1 because it’s the first in step choosing either standard (10ml) or high sensitivity (25ml) test

 

[AUSpool]

All good Yann, here’s what I would do. Do the FC first. If its over 10ppm add an extra drop of the TA buffer. - 3 drops for low res, 4 drops for high res. I always use the high res for TA.

 

[yann]

Cool no worries
Yeah I always use high res for TA, standard for CH and salt.
I'll switch off my SWG for the night and until I run my tests tomorrow. That should bring FC under 10ppm.

I'm really tempted by Borates, so I want to get my TA and PH in check before I add Boric Acid.

Roughly does anyone know how many cycles of low PH/aeration I need to bring my TA from 90 (last test) down to 60 (lower end TA for plaster pool under SWG)?

Cheers

 

[AUSpool]

It’s a bit hard too call for TA rotations to get to 60ppm from 90ppm. Very roughly ~8ppm each time but it reduces. Use PoolMath to estimate. I used your volume and assumed a pH of 7.8 to 7.2 with a TA of 90. That gives 650ml of acid and when that is put in the effects it suggests it will lower the TA by 8.9ppm. If you go ahead again from 7.8 to 7.2 with a of TA of 82ppm you now require 600ml of acid which will lower your TA by 8ppm.

 

[Brad_C]

I was nasty to my pool and dropped TA 30 points at a time, but I have an awesome aerator and it's all fibreglass.

 

[yann]

Does adding CYA affect TA levels?
I know it drops PH, after all it's an acid! (-0.4PH for +20CYA)
Thanks

 

[AUSpool]

Yes and no. PoolMath does not indicate it does in the effects section but CYA adds buffering in an uneven way, it is pH dependant.

 

[duraleigh]

Yes and no. PoolMath does not indicate it does in the effects section but CYA adds buffering in an uneven way, it is pH dependant.

I don't understand that. To my knowledge, CYA has no appreciable affect on TA and a fairly minimal affect on pH (but a little)

Can you explain further?

 

[AUSpool]

The question is “Does adding CYA affect TA levels?”

According to the ‘effects of adding chemicals’ in the old PoolMath page the answer is no or maybe it’s just not listed but according to ChemGeek the answer is yes, it does add buffering capacity. The cyanurate ion counts toward total alkalinity.

Chem geek wrote;
“Cyanuric Acid <---> Cyanurate Ion + Hydrogen Ion
where at a pH of 7.5, 82% is Cyanurate Ion and 18% is Cyanuric Acid. Cyanurate Ion also counts toward Total Alkalinity which is why it is adjusted in the calculations for the saturation index because what is needed for that formula is the carbonate alkalinity (carbonate hardness).”

“The cyanurate buffer system adds some buffering in an uneven way (when combined with the carbonate buffer system) as a function of pH.”

TA--What is it really?

 

[JoyfulNoise]

The TA of pool water is compose of three components - carbonate alkalinity, cyanurate alkalinity and, if present, borate alkalinity. The amount of “alkalinity” contributed to the TA by CYA is roughly 1/3 the concentration of CYA at a pH of 7.5 (it’s pH dependent). So, if you had a TA of 90ppm at a pH of 7.5 and no borates, 60ppm would be the carbonate alkalinity and 30ppm would be the cyanurate alkalinity. At a pH of 7.5, borates at a boron concentration of 50ppm only adds about 5ppm to the TA.

 

[AUSpool]

Thanks Matt, I was second guessing myself.

Does adding CYA affect TA levels?
I know it drops PH, after all it's an acid! (-0.4PH for +20CYA)
Thanks

Yes it does, very roughly at a pH of 7.5 one third (1/3) of your 20ppm CYA addition will increase your TA by ~6ppm and is detected and/or included as part of the standard TA test. The increase will be a little less as the pH increases and a little more as it decreases. Reducing TA using the acid aeration method will only decrease the carbonate alkalinity portion of total alkalinity. It will not reduce CYA or borate if present.

I’m with Dave in that I don’t think a 20ppm addition of CYA will increase the pH that much. Maybe immediately but once everything settles only ~18% (pH dependant) of that addition will be in the form of Cyanuric Acid.

 

[JoyfulNoise]

pH in a multi-component buffered solution is not a simplistic calculation to make. In pool water where carbonates, cyanurates and/or borates are present, the calculation for pH turns into a 4th order polynomial, multiple equation mathematics problem. It takes very sophisticated computational programming to get an exact answer.

Pool Math, like many of the industry lookup tables, relies on some shorthand’s and assumptions to greatly simplify the pH calculation problem. As such, it is only reliable over smaller changes in pH, about +/-0.4 units at best.

Cyanuric acid is a weak acid just as boric acid is a weak acid. Given the large concentration of carbonates in pool water, you will be hard pressed to see a measurable change in pH from the additions of small amounts of CYA. It also dissolves so slowly that it’s very difficult to see a change in pH. I simply would not worry about it.