I was unable to find this on the forum so if I have missed this please stir me to it...

Looking at an old log sheet from a Pool Service I had there Is a CYAf number in there....It has corresponding correction factors it looks like based on current PH value. What I dont know is what these numbers mean as a positive or negaitve value, multiplier, etc....

An example is CYAF--->PH7.6-0,33

Why is there a compensation factor for PH value and how do I use it for my balancing?

That is a correction factor for Total Alkalinity.

At pH of 7.6, Actual TA = TA - CYA*CYAf

So if you read your TA at 100, CYA at 100, and pH at 7.6 your actual TA would be 77.

It is used in the calculation of corrected total alkalinity. Corrected total alkalinity is used to compute the Langelier Saturation Index. Unless you have very high CYA levels the difference between TA and corrected TA is very small and can be ignored.
The correction factor is how much you multiply the CYA reading by and then subtract that result from the TA to get the corrected TA. The correction factor changes with pH but it basically works out to 1/4 to 1/3 of the CYA reading. If your CYA is 40 ppm this means the TA correction works out to about 10- 13 PPM. This is is about the precision of the test anyway so it really becomes moot. If you have very high CYA levels then the correction might be of some value.
Then again, if your CYA is high enough to create a large difference between the TA and corrected TA then you need to worry about lowering the CYA and not that much about your TA!

Okay I was way off, had thought it was a multiplier for the CYA and knew nothing about the correlation to TA. I happen to have a high CYA level (120 but keeping FC high, so far okay)

Just to verify the info I have is the correct multipliers for CYAf can anyone refer me to the math or a chart for this? Instead of a repost if its in a thread you can just point me that way and I will find it.

THANKS IN ADVANCE.

Since the correction factor varies with pH here is an easy way to figure adjusted TA.

If you pH is 7.0 to 7.2 then subtract 1/4 of your CYA reading from the TA reading.
TA ppm - (.25 x CYA ppm) = Adusted TA

If you pH is 7.4 to 8.0 then subtract 1/3 of your CYA reading from the TA reading.
TA ppm - (.33 x CYA ppm) = Adusted TA

Because of the inherent error in the measurement of these tests (the precision of the tests) your results will be close enought for government work!

Also be aware that the value of using adjusted TA is still a topic of debate in the industry with arguments supporting both points of view. Taylor Technologies seems to be one of the main supporters of using the Adjusted TA.

Personally, I find its usefulness a bit overrated in most circumstances (except when CYA values are well above 100 ppm, and in that case your TA and saturation index are NOT the problem you should be focusing on!)

Here in the forum we do not use the adjusted TA in our recommended levels.

I agree with Waterbear. I learned this and promptly stashed it away in the "things that have never helped me do my job better" file.

Even in the case of a TA of 80 and a CYA of 80 (at a pH of 7.5), the difference between using an adjusted TA vs. unadjusted TA only results in a saturation index difference of 0.16. The Pool Calculator does take into account the CYA in calculating the Calcite Saturation Index (CSI). As for arguments in the industry, the chemistry for calculating the saturation index would definitely say to do the adjustment since only the carbonates contribution to TA is relevant for determining saturation of calcium carbonate. I presume that the argument is solely around whether this sort of adjustment is practical, not whether it is technically accurate.

Richard

Exactly, as you pointed out in your example above.