Adjusted? Total ALk?

Hi,

It's been very, very hot here recently. To compound matters I had our heater fixed and the tech cranked the thermostat up which I missed. The pool is 92 degrees F now! I had a problem with algae but have kept it under control with Ben's kit and the BBB method.

In a moment of absurdity I took a sample of my water to the pool store thinking they could/would check for the presence/emergence of algae. I know, dumb move.

They couldn't but ran the water test anyway. They tested for Tot Alk and Adjusted Tot Alk. I asked the pool guy what exactly was "adjusted TA". He explained that had I had no CYA, both numbers would have been the same but that something having to do with the CL and CYA "adjusted" the ALK result. Of course, my resut was low with their test.

I'm running about 120 with Ben's 233 but only 80 on their Alex and 62 on their Adj Alk.

What gives and should I be doing something I'm not?

My other #s read:

FC - 4
CC - 0
TC - 4
pH - 7.6
Alk - 120
CYA 30
temp 92!

Thanks for the advice.

CoffeeBean

First I want to say that their numbers are bogus even for the ajusted alk!

The level of cya in the water will test as part of the total alkalinity even though it is not part of the carbonate/bicarbonate buffer system we are testing when we test alkalinity. There is a mathamatical correction that is applied based on pH and CYA level to be subtracted from the ALK to get the 'adjusted alk'. This supposedly more truely represents the amount of carbonate/bicarbonate in the water. The value of this adjustment seems to be the topic of some debate. Taylor Technoligies sees merit in it. Your pool guy was right in saying that if you had no CYA the ALK and Adjusted ALK would be the same. Personally, I don't think it matter much unless the CYA levels are above about 60 ppm since below that it really doesn't change th ALK reading very much. If you want to get a 'quick and dirty' adjusted alk reading then subtract 1/3 of your CYA reading from the ALK if you pH is 7.4 or above and 1/4 of your CYA if the pH is 7.0-7.2. You can see that if the CYA is above 60 ppm at normal ph (7.4-7.6) this means that it can affect the ALK reading by 20 ppm or greater... If you CYA is around 30 it really only changes it by about 10 ppm which is nothing to lose sleep over!
Hope this explains it.
The reason I say the Alex readings are bogus is that they are done with test strips and a reader. They have your CYA closer to 60 ppm than 30 ppm to get that much of a difference in the ALK and the adjusted ALK. I would trust the ALK reading from your drop baed kit. Your adjusted ALK is in the neighborhool of 110 ppm....perfect!

Waterbear,

Thank you for your reply and explanation. I guess I'm a confirmed "Ben-ite" now. I cringed when I saw him dunk a long test strip into a beaker of my pool water and figured the results wouldn't be accurate.

CoffeeBean