The case of the missing stabilizer

[dschlic1]

I am having trouble maintaining stabilizer levels in my pool. My pool was fill at the end of October, and to the best of my knowledge 3 lbs of CYA was added at that time. Pool volume is 7500 gallons.

Pool store testing results:
11/10/2007 60 ppm
11/24/2007 50 ppm
12/08/2007 45 ppm (1.5 lbs of CYA was added)
12/21/2007 45 ppm (again added 1.5 lbs CYA)

Test results using ColorQ:
12/18/2007 29 ppm
12/22/2007 46 ppm (at 2 pm)
12/22/2007 36 ppm (at 5 pm)

I also am testing with HTH 6-way test strips which have blocks for 0, 30~50, 100, 150 and 300. All tests match the 30-50 block.

According the the Pool Calculator website, the initial 3 lbs of CYA should have given a level of 48 ppm. The two following additions of CYA should have added 24 ppm each for a total level of 96 ppm. There does not appear to be a leak in the pool, I fill it about two inches once a week. Allowing for 10 to 15 % splash out over the two months, the level should be 86 ppm.

I know the readings can vary between testing systems, but tests within a given system should not vary that much. This leaves two options: There is something interfering with the CYA test, or something is destroying the CYA.

 

[duraleigh]

I am having trouble maintaining stabilizer levels in my pool.

From this quote above and your previous posts, I would lean towards your testing methods being the culprit......not the CYA.

Test strips are infamously erratic (although your strips appear to be the most accurate of the three methods you've used) and I would not consider them as particulary worthwhile esp. for CYA.

The issues with the ColorQ are pretty well documented by other posters on this forum.

The pool store COULD be the most erratic. You essentially put the testing method in the hands of someone who may or may not be qualified to perform the tests. Certainly not in every case, but I would tend to think of this as the LEAST realiable simply because you lose control of the method and outcome.

All the above said, even the most reliable (IMHO) test method (Taylor chemistry and your own hands-on testing) has some variance in it and I would consider +- 10ppm well within reason each time you perform this test.

I think the key to good CYA maintenance is to stick with whatever testing method makes you the most comfortable and use those results and watch for trends.....not differences between that test and other test methods.

Secondly, if the current test methods you are using are not reliable enough for you, consider the CYA test available from Taylor (Or, of course, TFtestkits). I think you'll see a big improvement in the consistency of your results.

 

[Guest]

Water temperature is a factor in the CYA test. Make sure your sample is between 70-80 degrees before testing! The drop you are seeing is consistant with water temperatures getting colder.

 

[dschlic1]

Water temperature has been stable. In fact last week when I first contacted LaMotte about the CYA test results, the first thing they said was my water was too warm! Of course cooling the water down did not help. Wednesday I will try and get the water tested at two other stores nearby. The last pool store test I have some doubts about the accuracy. I noticed that the utensils were dirty. Also some of the results were off. Never the less the amount all of the tests are off is quite large, on the order of 30 ppm.

 

[JasonLion]

The ColorQ is finicky about the CYA test. The water temperature needs to be exactly right and you need to let the sample sit for the correct amount of time after adding the tablet and even then it can be fairly imprecise. Test strips are totally unreliable for CYA testing. And pool stores can occasionally have problems doing even the reliable CYA test right.

Keep in mind that any form of water replacement (auto fill, rain, garden hose, etc) will lower the CYA level. I think I remember you saying that you needed to add salt recently, and if so you should have also added CYA at the same time. The salt test is more reliable and CYA and salt levels normally track together.

Even with all that your results do seem unusually low. A slow leak combined with auto fill would account for it and be fairly difficult to detect.

 

[dschlic1]

I do not have an autofill.

 

[Guest]

I do not have an autofill.

Please see my answer to you in your other thread on the SWG,

 

[duraleigh]

I should know better, but I'm gonna' restate my opinion on the missing CYA........I see nothing conclusive in the tests to indicate CYA has, in fact, been reduced.

Until you test consistently with a turbidity test and do your own testing, I don't think it's definitive that your CYA is disappearing.

 

[dschlic1]

I agree with duraleigh. The only way to solve this is to get tests from several different sources. This issue of tests being variable is a bit fustrating to me. I am an electrical engineer working for a systems integrator. I design, build and install instrument and controls systems, most of them for municipal water and wastewater plants. For me a test or measurement that is not repeatable, and accurate to stated limits is useless. In fact if I tried to install such a system, I would be in big trouble.

I am very much aware of the errors that incorrect procedures can cause. Last year I started up a control and instrumentation system in the largest surface water treatment plant in the southeast. This plant is capable of producing 150 million gallons of drinking water per day. We have over 350 online instruments installed in this plant. One of the primary reported online tests is filtered water turbidity at the discharge of the filters. The state limit is 0.1 NTU. The filters typically produced 0.05 NTU which is a the limit of measurement. The owner was checking the accuarcy of these instruments using a grab sample meter. The readings were not correleating. After re-calibrating the online instruments several times, I checked the procedures being used by the owner for the grab samples. It was incorrect. Once the correct procedures were used, the grab sample readings and the online readings were the same.

 

[duraleigh]

dshlic1,

The only way to solve this is to get tests from several different sources.

Not to be contrary, but, actually, I am saying almost the opposite. I am saying limit your testing to the turbidity test (done only by you) and do it two or three times a week or so apart. I think you'll find your results will be +- 10ppm consistently.

By using pool stores, test strips, colorQ and comparing against one another is somewhat like apples to oranges in a loose sense. Most importantly, those methods are the least consistent. You'll get your most accurate and repeatable results by doing it yourself with a turbidity test.

 

[Guest]

I gotta agree with Dave and I've been doing water testing of one kind or another for over 40 years now. (I've kept aquariums since I was a kid!) Strips are basically useless. Electronic testers are only as good as their calibration and their range (and the lack of range is a serious drawback to some of LaMottes testing, even in their expensive meters!). I can test my water right now with 4 different test strips, A LaMotte Waterlink Express colorimeter and LaMotte UDV dry reagents and 3 different 'disappearing dot' type CYA tests and all will give me different results except for the 'disappearing dot' tests and NOT all three of them are based on Taylor reagents. I know this is true because I have done this time and again. These three 'disappearing dot' tests give identical results.

 

[mas985]

My experience on CYA pool store testing has been that there is no consistency at all. I would get results back ranging from 30-80 ppm dending on the pool store and who was running the test. I was curious how well they did testing but soon concluded it was a waste of time.

So once you get the testing part figured out, here is something else to consider:

Both Chemgeek and I experienced CYA loss this year over the summer (50% reduction in 6 weeks). At first I thought it was a coincidence but we both live in the bay area which had experienced some fall out from forrest fires up north. I had a considerable amount of ash drop into the pool. I can't say for sure if that is why we had lost CYA over the summer or if the reason was the same for both of us. For all I know it could be kids peeing in the pool. :lol:

Anyway, I guess my point is that pools can lose CYA without spashout or leaks although I think it is fairly rare. Other factors can remove CYA although there are probably only very extreme conditions which can cause this. Some pools experience a loss of CYA over the winter due to extreme algae conditions.

 

[Guest]

I think the key factor here has been the loss of both salt and CYA. I would still bucket test to look for a slow leak.

 

[dschlic1]

Some updated information on my CYA issue. It looks like most of the CYA tests were wrong. In fact of all of the test performed, it looks like only three of them are correct!

On 12/26/2007 I returned to my local pool store and brow beat them a bit about the last inaccurate test they performed several days before. Maybe because of this, they did a more accurate test, and came up with a CYA level of 100 ppm. This is close to the value calculated via dosing.

So I guess the moral to the story is do not put too much faith in CYA test!

 

[duraleigh]

So I guess the moral to the story is do not put too much faith in CYA test!

Nope. The moral here is that until you do your own testing with a TURBIDITY test, whether it's mine or someone else's, you are wasting a lot of valuable time (since November) and spinning your wheels testing your CYA the way(s) you have been.

 

[ivyleager]

So I guess the moral to the story is do not put too much faith in CYA test!

Nope. The moral here is that until you do your own testing with a TURBIDITY test, whether it's mine or someone else's, you are wasting a lot of valuable time (since November) and spinning your wheels testing your CYA the way(s) you have been.

Can I get an AMEN?!

 

[Guest]

So I guess the moral to the story is do not put too much faith in CYA test!

Nope. The moral here is that until you do your own testing with a TURBIDITY test, whether it's mine or someone else's, you are wasting a lot of valuable time (since November) and spinning your wheels testing your CYA the way(s) you have been.

Can I get an AMEN?!

Amen and Hallelujah!

 

[SeanB]

Donald (dschlic) has asked to be removed as a member, which I will oblige. I wasn't really following this thread and have to admit, we've been a bit harsh here and I can't really blame him for his frustration.

No doubt the advice given has been spot on, and based on LOTS of prior experience, but the harshness was probably a bit over the top. Sometimes things that may be painfully obvious to us, may take a while to set in for others.

While, there was some repetition of question and answers, I don't think this thread was without merit. Certainly others will learn from Donald's experience and questions.

My advice would be to simply refer posters back to the prior answer without the additional piling on.

Donald, if you happen to read this, I do hope you realize those very qualified responses were given to you in the spirit of mutual cooperation, and free of charge. I never cease to be amazed at the generosity of the members here who are willing freely give their time, even when it means answering the same questions over and over again. So I hope that you understand their frustration as well. You were give the same, correct answer multiple times, and failed to act on the advice - so the street really does go both ways.

Our bias here is not for a particular brand of test, just for accuracy. The more accurate your test results are, the more accurate your answers will be. I'm sure we can all move on from here, so if you do decide to continue as a TFP'er, just send me an e-mail and I will happily re-instate your account.

Sean