CYA Puzzler - Jumped from 60 to 100

[phalcon51]

Back on May 8th I tested my CYA level with both the Taylor K-2006 and the Blue Devil CYA test kit. They both read about 55-60 ppm. Using the Pool Calculator app on my iPod it recommended adding 2 lb. 3 oz. to my 26,200 gal. pool to raise CYA from 60 to 70 ppm. I put 2 lbs of Leslie's Conditioner (99% CYA) in a sock and suspended it from the skimmer cover. Today, 7 days later, all the CYA is dissolved from the sock so I rechecked the level, again with both kits, and it's reading right around 100 ppm. I even had my wife test it without telling her what my readings were and she came up with the same numbers.

Why would it rise so high? Is the Pool Calc app incorrect?

Btw, Pool Calc says I'd have to add 6 lb. 9 oz to go from 60 to 90.

Thanks for any help,

Gary

 

[Bama Rambler]

It's more likely that your pool size is incorrect and/or you started with more that you thought. It's probably a little of both.

 

[phalcon51]

I don't think so. I took the pool measurements pretty accurately to determine the pool size. I even took into account the little cutout in the shallow end where the steps are.

A week ago when I checked the CYA level I also did it with both testers, did it multiple times to make sure of the reading and had my wife check it that time as well. She came up with the same level, about 60 ppm, that I did. If anything, 60 would've been on the high side.

I really don't think there's anything wrong with my measurements or my testing routine.

Gary

 

[JamesW]

The cyanuric acid test is somewhat unpredictable. I can test the same pool twice in the same day and get different results, sometime as much as 20 ppm.

 

[HouTex]

I think the CYA tests are inherently inconsistent and unreliable. My pool was finished in early December 2010 and I started with trichlor pucks. After using about 9 or 10 pucks my pool store's tests said my CYA was 100. I drained half the water and refilled the pool and switched to bleach. After about six weeks of that I decided to install a SWCG and I've been using the SWCG for about two months. During this time the pool store's measure of the CYA has been all over the place. It intially went down to 50 as expected. I then added more CYA to get it up to the recommended 80 ppm for the SWCG and the pool store's test showed 100--which seemed way too high. I then began testing the CYA myself with the TF-100. The initial test result was 40! In hindsight 40 was probably fairly accurate considering the 9 or 10 pucks I added plus the additional amount of CYA i added. I added liquid CYA to get it to the recommended 80 ppm and now several tests only show that the CYA is 60-70 tops. My conclusion is that the pool store's results were clearly off. Nine or ten 3" pucks should not have raised the CYA to 100 in 2.5 months as their tests apparently showed. However, the amount of liquid CYA I added should have raised the CYA to 70 or 80, assuming the TF-100 kit accurately measured CYA. But several tests showed that the CYA is more like 60 or 70 vs. 80. Bottom line for me is to do you own CYA tests, but know that it's not exact.

 

[duraleigh]

Keep in mind that the CYA test is accurate roughly plus or minus 15ppm. That said, after having done it a lot over the years, I consistently get the expected result to within 10ppm.

A word of caution.....calculate and dose carefully......and then be patient for the results. CYA testing needs several days after addition to be valid.

To my knowledge, all the CYA tests use the same turbidity testing method so they should all report the same result. The larger view tube that ranges from 20-100 does provide for some increased accuracy, IMO.

 

[phalcon51]

Well, I waited 2 weeks before I measured the 60 ppm and I actually did it twice on subsequent weekends and got the same result, again with both testers. So it seems that I was getting consistent readings at the previous level. That was also under somewhat different lighting conditions; a little overcast in the morning vs. bright sunlight in the mid afternoon. I guess I'll try reading it a couple more times during the coming week and see if I consistently get the same reading.

A word of caution.....calculate and dose carefully......and then be patient for the results. CYA testing needs several days after addition to be valid.

That's why I only added enough to raise it from 60 to 70 and then waited a week before I tested.

Even with the +/- 15 ppm accuracy I'm reading way over that at +30 ppm with today's test.

Gary

 

[chem geek]

By any chance, was the water cold when you did the earlier tests? Colder water takes longer for the CYA test to form a precipitate, not just 30 seconds that is recommended. One can either warm up the sample to room temperature or give more time for the test.

The 2 pounds of CYA in 26,200 gallons should have only raised the CYA by around 9 ppm so a 40 ppm rise is indeed very strange. The Leslie's Conditioner appears to come in 4 and 8 pound containers, so you added half of a 4 pound container, for example?

 

[phalcon51]

No, I actually weighed out 2 lbs. on a digital scale. As long as the tools are available like the pool calculator, reliable test kits and digital scales I try to do this stuff as accurately as possible so as not to have surprises like this. But I guess stuff happens no matter what precautions you take.

The water temp has been about 68-72 degrees in the mornings when I check it for the past few weeks and of course warmer as the day progresses up to a max of 77 so far.

Gary

 

[TravisD]

I had a weird experience a while back with Leslie's stabilizer, only it was the opposite effect. I put in 4 pounds which will usually take me to about 40 and my level did not increase hardly at all. It was very odd. I bought a 4 pound container from another pool store nearby ($10 cheaper too) and it brought it up exactly to 40. I never figured out what happened, but I will not buy stabilizer from Leslie's anymore.
In fact, I started a thread about it and it seems I am not the only one who has had trouble with Leslie's stabilizer.

 

[chem geek]

Well, I'm sorry you both had such weird experiences with the Leslie's stabilizer. Though measuring low could be a stabilizer that had fillers or had degraded, I don't know how it could increase CYA by more than what was added. Very strange...