A discussion of CYA turbidity

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duraleigh

duraleigh

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It's my feeling that a sort of "urban legend" is taking a foothold on the forum. There have been others in the past and, because they get repeated, they become accepted.

First, I am not asking for you to prove me wrong. Like everything in this world, there are exceptions to the norm.......I'm interested in discussing only the day to day testing we do in our pools.

Anyway, the "legend" I'm concerned about is innaccurate CYA testing because of algae in the pool (or cloudy water). I think we're throwing that out as a reason much too often.

I have taken my view tube down to my pond (few, if any of you would swim in that water.....visibility is about 12") and when I gather a sample into the view tube, it is as crystal clear as my pool water. If my view tube had a 10ppm mark, the pond water would not come close to obscuring the black dot at the 10ppm mark.........not close at all.

So, when most folks say thay have cloudy water, it is my thinking they are talking about water that is no more turbid than my pond water and probably much less. In other words, I believe cloudy pool water would generally have less than a 10ppm affect on CYA test results and that's within the margin of error to begin with.

If I'm overlooking something (please don't dream up some wild-eyed scenario) please post it and continue the discussion. Try it yourself. Find a puddle of water or some source that looks murky to you and see how much you have to put in to get a 20ppm reading (or close enough to skew the test).....I think you'll be surprised at how cloudy your water will have to be.
 
Thanks Dave, for bring it up, and I was wondering it myself but not ambitious enough to try it. That very subject has come up a lot this week and I found myself making the filter recommendation several times....being completely unsure as to the actual amount the CYA test would be off by, if any, 10, 20, 30ppm? I had no idea, just throwing the suggestion out there and not knowing if it would make a difference either way. That one guy drained his whole pool..... :shock: and we had no idea what his CYA actually was!
 
here's a quote from a post a while back about my results:

I mentioned this in my "Algae Diary" post, but I thought it deserved some attention on its own. I opened with algae this year, and my first water test showed a dramatic decrease in TA, but CYA was at about the level of last summer, 35ppm. This puzzled me because if the TA had dropped, that indicated major dilution from rainwater over the winter, but CYA should have been affected the same way.

Now that the water is clear, I retested the CYA and found it to be less than 20. I had suspected that the presence of the algae and dirt from the winter had affected the CYA turbidity test. Waterbear felt that this was the case as well. Apparently that is confirmed. Interestingly, the pool water without the CYA reagent seemed very clear in the CYA test tube, with the dot clearly visible and sharp, even when the tube was full.
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The pool was darker than it's ever been, but the water in the sample bottle was very clear in appearance. I think the presence of suspended solids can't help but influence the results of a turbidity test. Since the turbidity test appears to be non-linear based on the spacing of the markings on the tube, a small amount of additional turbidity seems like it could skew the results significantly.
 
Somebody with a SWCG could answer this pretty easily by taking two water samples from their pool and diluting one sample with distilled water and one sample with soupy pond water. CYA reading for the pond water would be higher if algae/dirt affects the reading, and they'd be the same if it doesn't.

Slight deviation here Dave, but can you get the fancier CYA test tubes where you raise the disc until you can see it? Does that type use more reagent? Seems to me that I could get a better read with one of those.
 
Somebody with a SWCG could answer this pretty easily by taking two water samples from their pool and diluting one sample with distilled water and one sample with soupy pond water. CYA reading for the pond water would be higher if algae/dirt affects the reading, and they'd be the same if it doesn't.
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John, that would seem to be a plan......it's not clear to me why I couldn't do the same thing....even tho I dont have an SWG.
 
I remember one or two people who tried the coffee filter approach and got numbers that were about 20 lower than without the coffee filter. Five or ten people have posted CYA numbers before and after defeating algae that differed by at least that much. The test is a bit variable even without complications, so it is difficult to say how repeatable those results are.
 
duraleigh said:
John, that would seem to be a plan......it's not clear to me why I couldn't do the same thing....even tho I dont have an SWG.
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I figure the higher CYA in a SWG pool would lend itself better to the dilution. Even 50ppm is probably enough though. You should see two 25ppm samples with 50% dilution. Lower CYA might result in diluted samples that wouldn't register on the comparator.
 
Another possible reason for the differences in the readings is due to the "algae" eating the stabilizer. Typical scenario: Pool owner finds a white turbid pool, checks CYA to find shock level. CYA measures 40 ppm. Shocks the pool, meanwhile the bugs are munching away on the CYA. Poll finally cleans up, pool owner checks CYA again. Finds the new value at 20 ppm. Probably 15 ppm loss was due to the bugs :lol:
 

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New2Me said:
Just wondering how the "computer test" for CYA is done, is it an opacity, or transmittance test of turbidity? Any chemical people aware of a more precise method?
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Unless it's strips in a reader :shock: it's the same turbidity test that is manually done, just read with a colorimeter/turbidimeter. That is how we do it at work. As far as it goes I test a lot of pools and have a lot of people come in when they have cloudy and/or green water. I can attest that CYA will read higher when the water is cloudy. Our unit is supposed to read a 'blank' first to take into account any cloudiness in the water but we cannot get the unit to read when the water is green or cloudy from algae and I have to do manual testing with a Taylor kit.
Also, I have on numerous occasions, places a vial of tap water in as a blank and ran a vial of pool water to see if the CYA test is affected. I have gotten readings from 10 to 35 ppm on the CYA test (this is with NO reagents, just the cloudy water)! The reason I did this is because I was noticing an apparent CYA drop in pools that came in for testing when they had algae outbreaks vs the readings I got once the algae was dead and the pool cleared.

I am very satisfied from my own experimentation that when the pool is green or cloudy with algae then CYA testing is NOT going to be accurate and will read high!
 
dschlic1 said:
Another possible reason for the differences in the readings is due to the "algae" eating the stabilizer. Typical scenario: Pool owner finds a white turbid pool, checks CYA to find shock level. CYA measures 40 ppm. Shocks the pool, meanwhile the bugs are munching away on the CYA. Poll finally cleans up, pool owner checks CYA again. Finds the new value at 20 ppm. Probably 15 ppm loss was due to the bugs :lol:
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Algae does NOT eat CYA. CYA is consumed by anerobic (oxygen hating) denitrifying bacteria that are commonly found in soil. For this to work the pool MUST be stagnant because any circulation would increase the oxygen and the bacteria would die! This is why CYA sometimes disappears in a closed pool during the winter. The water is NOT circulating and is stagnant so the aerobic bacteria can grow. Also, this is a slow process and does not happen in the matter of just a week or two.

The effect you are talking about above is from the clouding of the water from the algae and it's interference with the CYA test!

I rest my case!
 
duraleigh said:
It's my feeling that a sort of "urban legend" is taking a foothold on the forum. There have been others in the past and, because they get repeated, they become accepted.

First, I am not asking for you to prove me wrong. Like everything in this world, there are exceptions to the norm.......I'm interested in discussing only the day to day testing we do in our pools.

Anyway, the "legend" I'm concerned about is innaccurate CYA testing because of algae in the pool (or cloudy water). I think we're throwing that out as a reason much too often.
.
Click to expand...

Sorry Dave,
Have to disagree with you. You are just plain wrong here. I have done experiments on my own already and will stand by what I have said because it is repeatable and I have seen it time and again!
 
duraleigh wrote:
I have taken my view tube down to my pond (few, if any of you would swim in that water.....visibility is about 12") and when I gather a sample into the view tube, it is as crystal clear as my pool water. If my view tube had a 10ppm mark, the pond water would not come close to obscuring the black dot at the 10ppm mark.........not close at all.

What tube did you use? Mine "top out" at 20 ppm. Guessing by the exponential expansion of the markings on the tube, it would have to be quite tall to get to zero! If your pool is crystal clear, could you set the tube on the bottom of the deep end and still see the dot? I bet you can. Anything (air bubbles, skin flakes, dead algea, urine, oil, etc..) that reduces the ability to see the dot (or main drain?) has increased the turbidity, or clearness, of the water that might not register in a 7 ml sample. If you have a 25,000 gallon pool that you haven't added 25,000 gallons of R-0013 to, haven't mixed for 30 seconds, have let sit for more than 2 minutes, and you can't see the bottom, then you have turbidity to start with! Now add the r-0013, mix, and see how much murkier it gets.
 
JohnT wrote:
Somebody with a SWCG could answer this pretty easily by taking two water samples from their pool and diluting one sample with distilled water and one sample with soupy pond water. CYA reading for the pond water would be higher if algae/dirt affects the reading, and they'd be the same if it doesn't.
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John's idea seemed very doable to me so I thought I'd try it.....even tho my CYA of 40 wouldn't give us quite as definitive an answer as someone with CYA of 80ppm. So.......

A. One cup of pond water (with plenty of mosquito larvae and floaties) with a visibility I would estimate to be about 16".

B. One cup of pool water

C. Test Kit

First Test:

1. First confirmed pool sample of CYA 40.....result........CYA 40ppm

2. Next, filled CYA mixing bottle with 1/4 pond water, 1/4 pool water and 1/2 CYA (R-0013).....Result....20-25ppm

3. Then, rinsed all and filled 1/4 tap water, 1/4 pool water, and 1/2 R-0013.....Result.....20ppm

(Okay, let's do it again and this time be very, very accurate)

Second Test:

1. Reconfirmed CYA of 40ppm in pool by repeating standard CYA test.....result......40ppm

2. Next, filled CYA mixing bottle with 1/4 pond water, 1/4 pool water and 1/2 CYA Reagent.....Result....20ppm

3. Then, rinsed all and filled 1/4 tap water, 1/4 pool water, and 1/2 R-0013.....Result.....20ppm

At first blush, the validity of John's method would appear pretty good. I'm sure there are some scenario's under which it may not hold up, but I'm not smart enough to figure them out and I'm not sure those scenarios would exist in a typical pool.

One last thing.......I certainly hope the upcoming replies proving me "just plain wrong" again (and I very well may be....this is a discussion, not a "smartest guy in the room" contest) will contain an increased tone of civility. My feelings are easily bruised :shock: :shock:
 
I apologize for any comments that I have made that have not been civil, I meant no harm. I am usually smart enough to know that I am NOT the smartest one in the room, but sometimes my mouth (er, fingers?) thinks otherwise! :oops: And especially here on TFP, where there are so many helpful people, you make this the best site I've been to! :oops:
You have Taylor on your side, too! From their website:

Potential Interferences for Kit Number: K-1721
There are no potential interferences.

They are the most trusted name in water testing, so maybe we should just trust them, and go -
Enjoy a GREAT WEEKEND in the pool!
Best to All! :)
 
First of all, from a straight turbidity point of view, the test is logarithmic as was pointed out earlier. If you take pool water before adding reagent and you measure something higher than that of clean pool water or distilled water as a reference, then it will increase the turbidity of your CYA test and will do so roughly by the amount you measured as if that "ppm" amount were added to the CYA "ppm" (this works, even in a logarithmic test, since both test measurements are logarithmic and convert to concentrations which are an additive space -- the logarithmic part of the test accounts for the multiplicative effect of distance and absorption of light -- the two light measurements in absolute transmission level would not be additive).

So I don't know why some measure turbidity levels while others do not, though having a level of less than 20 would certainly be possible in any event since that's the limit on the TF100 test. Even water that looks clear could be at least 10 ppm.

There is another possibility and that is that water with algae in it has many more particles for nucleation of precipitate so *maybe* the CYA test gets a non-linear effect in CYA ppm apparent concentration by having the CYA clump more readily onto algae rather than be dispersed in the "standard" that occurs from shaking it for 30 seconds. Maybe that reduces transmission more than would be accounted for independent concentration alone. That's just pure speculation on my part.

Richard
 
Hey, Richard,

Assume you have sample (pool) water that was so murky it measured 20ppm in the view tube prior to adding R-0013.

You also knew that the calculated amount of CYA you put in the pool was 40ppm.

When you add the CYA reagent to that sample, do you feel the test would return 60ppm?
 

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