CYA test observations

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cwuffman

cwuffman

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Jun 27, 2012
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The Woodlands, TX
On another thread I mentioned that I had out of curiosity compared my results using the TF-100 kit and those of a local pool store (Leslies). We pretty much agreed on all but the CYA test.

Immediately after draining and refilling:

Pool store: 30 ppm
TF-100: <20 ppm

After using trichlor tablets to raise CYA:

Pool store: 45 ppm
TF-100: 30 ppm (or thereabout)

Both are acceptable numbers, of course. After realizing from other threads on this site that the test is based on equal ammounts of pool water and test reagent I questioned whether or not I was properly filling the included test bottle. I then repeated the test using one of the other measuring cylinders in the test kit and measured out 14.6 cc (I think that is what is indicated on the mark I used) of each pool water and reagent. The results as observed by my wife and me were now 45 ppm. It appears as if the previous tests were due to "operator error".

Actually, based on an "after drain" reading and the calculated (per pool calculator) ppm value I should have achieved using the number of trichlor tablets used, the final ppm value should be somewhere in the mid 40's.

Anyway I now have a bit more confidense in measuring each component rather than using the pre-marked bottle. Has anyone else had this experience?

By the way, I am by no means attempting to insult or blame the test kit. It's the best one on the market. This "operator" just needed some adjustment.
 
cwuffman said:
After realizing from other threads on this site that the test is based on equal ammounts of pool water and test reagent I questioned whether or not I was properly filling the included test bottle.
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I'm not clear on how you would have done this. Was the sticker affixed to the mixing bottle incorrectly?
 
Bjarni said:
I'm not clear on how you would have done this. Was the sticker affixed to the mixing bottle incorrectly?
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I am not really sure. I may play with the bottle and some water to see how I could have been incorrectly filling it.

I have been in the chemical industry since 1972 and just feel more comfortable using a graduated cylinder. Since I now realize (Duh!) that the stabilizer test uses equal volumes of pool water and reagent, it is easier for me to be comfortable with my results.

This website has been sort of an epiphany for me. The obscure pool industry "magic" is gone and been replaced by logical and repeatable chemistry.
 
Keep in mind that you can mix any quantity of the two liquids - as long as they are equal amounts. You need to mix enough to fill the tube to the expected cya level plus some in case the levels have dropped lower than expected.
 
This website has been sort of an epiphany for me. The obscure pool industry "magic" is gone and been replaced by logical and repeatable chemistry.
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As it has been for virtually all of us who have taken the time to become engaged with the education available.

That's a great statement, cwuffman. Concise and true.
 
So if I'm reading this right, instead of using the provided plastic fill bottle - filling to the bottom & top of the label - you're just using one of the provided graduated cylinder to perfectly fill each to the precise same levels ?? Then you pour that solution into the CYA cylinder ? Interesting ... I'm wondering if that may be my issue as well - and in fact why Leslie's came up with CYA=90 while my TF-100 testing is 45-50 ... hmmmm.
 
I'm wondering if that may be my issue as well - and in fact why Leslie's came up with CYA=90 while my TF-100 testing is 45-50 ... hmmmm.
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The CYA test is, in fact, a 50-50 mix of pool water and R-0013 reagent. If that is how you are preparing the solution, I would suggest Leslie's is the most likely suspect for error.

I am trying hard to understand how the difference in your test and Leslies relates to the 50-50 mix but I can't get it.
 
cody21 said:
So if I'm reading this right, instead of using the provided plastic fill bottle - filling to the bottom & top of the label - you're just using one of the provided graduated cylinder to perfectly fill each to the precise same levels ?? Then you pour that solution into the CYA cylinder ?
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Yes that's how I read this also.

cody21 said:
Interesting ... I'm wondering if that may be my issue as well - and in fact why Leslie's came up with CYA=90 while my TF-100 testing is 45-50 ... hmmmm.
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Unlikely... more likely testing error on their part or your part plus the +/- 15ppm error band.
 

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In response to Cody21, my technique (as of right now) is to measure equal volumes of pool water and reagent using the cylinders, making sure I have enough total volume to accomplish my expected CYA range (less liquid for higher CYA concentrations), probably 14 or 15 cc's each for my situation. I pour both into the supplied bottle and shake per the instructions (the small nozzle makes it easy to later tranfer it to the CYA test tube). The whole key for me is finally understanding the process and chemistry. Some people are quite content with a step by step recipe. Others like to know the science so they can manipulate it. I like messin with stuff.

I think a part of my previous difficulty may have been less than perfect lighting conditions.

As it turns out, all of the stuff on this thread and probably on my previous threads has already been clearly laid out by others on this website. If I would have just read more, I wouldn't have needed to post at all. But then I would remain a "New User" forever. And how fun would that be?
 
Last night out of curiosity I did a check on the volume of the CYA test bottle in my text kit. To measure volumes I used the included test cylinder with markings to 40cc and water for a test medium. Measured water levels were based on the bottom of the meniscus. Tests were repeated twice to confirm accuracy.

Test bottle filled to the bottom of the label then poured into measuring cylinder = 12cc
Test bottle filled to the top of label = 28cc

Test bottle filled to the bottom of the label twice and each time poured into cylinder = Just over 25cc total

I think there are three conclusions from this test:

First, the label on the test bottle is slightly low yielding a test mix of a higher ratio of reagent than pool water. This would result in lower than expected CYA values (as observed).

Second, it seems the 40cc measuring cylinder included in the kit is a bit inaccurate (2 X 12cc is not equal to a little over 25cc).

Third, the author of this thread is excessively anal retentive, and probably doesn't have many friends.
 
Wow .. That's interesting ... I mean given that the whole ratio thing in the "table" of CYA to target CL is so specific as to what our range should be. I would think that our measurements should be more consistent & precise ... I think I'll try your cylinder approach next time; just as a sanity check.
 
Bloomfield: what are we drinking?

cody21: it changed my readings from around 30 to around 45. (I'm afraid Chem Geek is gonna jump in here and tell me my numbers are off! Oh well, I can stand to be corrected.)

How many posts does it take to get past this "New User" ranking?
 
15 ppm is already the expected +/- on the test. Per Chem geek the chart is conservative enough this is a non-issue.

However if the test has +/- 15 AND the process adds more potential error then it may be an issue.
 
The mixing bottle provided in the TF-100 is a convenient but not laboratory precise way for you to get a 50-50 mix of CYA reagent and pool water. The label should be positioned on the bottle so that the top of the label roughly touches the topmost point of the vertical side of the bottle. That yields very close to a 50 -50 mix but it may not be perfect.

If your label is lower than that, please PM me your name and we'll fix it. You could also make your own mark giving you a 50-50 mix if you chose. You could also use a syringe or graduated cylinders but there really is no point.

The accuracy of the CYA test is generally plus or minus 15ppm so absolute precision on this test is not possible, necessary or important.
 
Thanks Dave,

No need to send a new bottle. I prefer in this case to measure equal parts of each component. I'm happy.

Again, great site, service and products. I'm having so much fun I'll probably wander through the neighborhood checking all of the neighbors' pools. Then I'll be back for more chemicals.
 

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