Accuracy of TFTkits Vials May be in Question...

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If the concern is that FC might drop below minimum for your CYA, which is the only possible concern I can think of, then simply raise FC by 1 or 2 ppm and make that your new daily target. It is a one time addition and your pool won't use more chlorine daily than it already does. I have long kept my FC above target for my CYA because we live in the woods and lots of things happen in my pool. Remember, chlorine is your friend, more is always better than less, and it is safe to swim with FC up to shock level for your CYA, [FC/CYA][/FC/CYA].

And who is to say which vial is correct? Or which syringe? Maybe they are all off? They are probably all off by a some amount. Is there a problem with the pool? Or is this just a question about which vial is most accurate? Pick the one that you like the best and use it every time and try to be consistent in your method and your pool will be fine. I'd rather be swimming!
 
KarenNJ said:
So it doesn't matter if the cylinders are not matching other equipment because they were made specifically to be used with the regents in the test kit? So, as long as we follow the test kit instructions and use those cylinders included in the kit we are getting accurate results? Don't compensate for the difference?
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No, if that were true you would not be able to depend on the accuracy of reagent refill bottles.

Just choose a procedure and stick with it. Use the mark on the vial and always use the same vial and the same reagents and that is as accurate as you are going to get with any given kit. Or use a syringe and always use the same syringe with the same reagents and the same is true. It is the state of the art.

Mike.
 
pooldv said:
If the concern is that FC might drop below minimum for your CYA, which is the only possible concern I can think of, then simply raise FC by 1 or 2 ppm and make that your new daily target. It is a one time addition and your pool won't use more chlorine daily than it already does. I have long kept my FC above target for my CYA because we live in the woods and lots of things happen in my pool. Remember, chlorine is your friend, more is always better than less, and it is safe to swim with FC up to shock level for your CYA, [FC/CYA][/FC/CYA].

And who is to say which vial is correct? Or which syringe? Maybe they are all off? They are probably all off by a some amount. Is there a problem with the pool? Or is this just a question about which vial is most accurate? Pick the one that you like the best and use it every time and try to be consistent in your method and your pool will be fine. I'd rather be swimming!
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I agree to your post. I personally am not comfortable hovering +1ppm above my target FC. I keep my FC 3-4 PPM above target and rest easy. Yes, I may burn off a little more chlorine during the day, but liquid chlorine is the cheap, and easy part of pool maintenance. Why make it more complex than it needs to be.
 
I like using a syringe only because it is a lot easier to expel what you don't want from a syringe and hit the same line every time than it is to fill a vial to the same line every time. I'm sure that I'm getting a lot more consistent sample size and it's fast and easy to do.

Mike.
 
Seems to me, if you have been using the same method and same bottle for testing and have not had any problems, why worry about it. I was completely new to all this last year, and using my TF100 Kit, I have not had any problems with my pool. I have had a lot of questions about things, and some say I may be a little anal, but my pool is right on target, and sparkling everyday. I can look at my water now, and tell if something is changing. Love this site, and my test kit!!
 
mikefamig said:
The OP is talking about a 2ppm discrepancy measuring chlorine and that is significant to me. I agree that consistency is more important to me than accuracy but if I want +-1ppm accuracy I can use paper test strips which are cheaper and easier to use than a liquid test. Accuracy is the reason that I'm willing to spend more time and money on a water test kit.

Until i hear differently I'll use a syringe to measure the sample assuming that Taylor is calibrated to a 10ml sample and that their plastic vial is just not made accurately.

Mike.
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That 2ppm is not globally true. In fact, the difference between 10ml and 11.5ml is 15% ... at a typical maintenance FC level the difference would be < 1ppm. Now at shock level FC, you could have a greater ppm difference, but that does not really matter as there is buffer built into the recommended levels.

Bottom line, I completely agree with Dave ... it is much more important to be consistent.

I completely disagree that you can get a +/- 1ppm accuracy from a test strip though.

And I think people are forgetting that the Taylor tests have an accuracy to them as well. IIRC, they state the test is only good to +/- 1 drop or 10% of the final ppm level, which ever is larger.

There is no issue with using a syringe or getting higher end vials to be more accurate with your water sample size ... but at the same time are you ensuring that all your drops are 100% consistent ... and you have your pool volume 100% correct ... and you know the strength of your bleach exactly?

There are a lot of sources of inaccuracy and I think this is being blown way out of proportion ... it is a pool, not rocket surgery :mrgreen:
 
OTPirate said:
The TFTestkit cylinders were upgraded about a year ago to have 1 ml line gradations apart for easier reading. The cylinders are designed to measure the same as Taylor Technologies cylinder (9198) as TFTestkits only uses Taylor reagents. They are not designed to be measured against medical instrumentation. TFTestkits cylinder - YouTube
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Interesting that the new TF-100 have 1mL graduated lines. My test kit was given to me as a gift in December 2016, so probably purchased in Nov/Dec 2016. I cant confirm where it was purchased, but the kit does have the 5 mL graduations.

I can say that both the test vials (not CYA), read the same volume. Both are not "accurate" to the realistic volume and more than 10 mL of liquid is need to get to the 10 mL mark. I have a oral syringe from a local pharmacy that I use to pull the 10 mL and I forget about the cylinder lines. I questioned which was more accurate, but in reality, I'm just looking for consistency.

But the difference in accuracy between 10 and 11.5 is ~15% depending on which one was correct. And not just with FC, but TA and CH.

Lets not criticize or trivialize the issue. In my opinion 15% is a bit large and can be improved upon. Saying that the kit would cost more to make an accurate vial is not really reasonable. I'd hazard to say it would cost the same either way. The vial mfg could make the same argument. I'm repeatable, just not accurate. Suggesting no not keep low level FC isn't the issue at question.

A big beef this forum has is with inaccurate pool store testing. Repeatability isn't really the question here. I think that the tests are very repeatable. But how can we really turn a blind eye when someone points out that one of the fundamental tools may have to be looked at? Have the new version of the vials been checked?

FYI, a shot of my vial in use (forget about the odd test results from a previous thread)

2eqfa5k.jpg



.

.
 
I hear you Dave, that it should not cost more to have the lines printed on the vials in the correct spot. There may be a manufacturing issue that is resulting in lines being slightly off, although perhaps they are still within specifications for the price point?

I think the cost difference per vial between the TF-100 and the Taylor vial is around $3. To change out the 2 vials in the TF-100 for the Taylor vials would be approaching a 10% increase in kit cost. Is it worth a 10% price increase for something that really does not have a meaningful impact on the pool maintenance?
 
I agree with teal that repeatability <> accuracy. That said, I also agree with others saying that it's not all that impactful to the end result. However, this approach prides itself on ACCURATE owner-performed testing. Accuracy is akin to precision in my mind, and this finding unfortunately raises questions around that precision, regardless of which vial is technically "correct". It's certainly not going to stop me from using my TF-100 or the vial that came with it, as I'm comfortable and have experience with it, but it can undermine the confidence in the overall approach for new folks joining the forum. I love TFP and tout it to everyone I know, and that's not changing from this... Just posing an observation.
 
FattyLumpkin said:
Accuracy is akin to precision in my mind, and this finding unfortunately raises questions around that precision, regardless of which vial is technically "correct".
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This is not correct. Accuracy and Precision are totally separate concepts.
The precision of the TF-100 vial and the Taylor vial are identical. Think of precision as the grouping of repeated test results. The test is very repeatable regardless of the vial.
It is the accuracy compared to "truth" that is impacted by the graduation lines and being discussed.
 

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Thanks for clearing that up for me, apologies for the mistake. Not trying to be argumentative, but I wouldn't say they're "totally separate concepts" in the context of this discussion, as what we're talking about is the precision of the measurement of water in relation to the accuracy of the results gleaned from that measurement -- or do I have that wrong as well? Regardless, I think the concept still holds true that any question around the accuracy *or* precision of any component of the testing may undermine a tenet of the approach and lead to a reduction in confidence. Maybe an overreaction on my part?
 
My goal here wasn't to cause controversy, but to point out a difference and/or error between an actual liquid-measuring device (i.e. a graduated cylinder) and the TFTkit vials vs. the Taylor vials. I think that as long as you're comfortable always measuring the same amount of water into the Chlorine and/or clear TFTkit vials each and every time, then you should be okay, as each test is relative to the next.

However, my problem is that measuring exactly the same amount of water into the vials was not working for me. Thinking there was a meniscus, I always added a few drops more of pool water above the 10mL line. However, with these types of vials, the meniscus is very slight, if not downright invisible to the human eye. So this obviously introduced my own error into my measurements each and every time...with some of the tests being inconsistent from the next, even if done subsequently as a double-check!

So I did another experiment tonight...

Personally, I think the CH test is the most "no-brainer" of all the tests, so I performed said test twice in the same vial. The first test was 10mL of pool water measured from the graduated cylinder (GC) and then poured into the vial, being careful not to splash and create droplets on the side. The second test was 10mL of pool water filled into the same vial and eyeballed right on the 10mL mark. NOTE: I did not go over the mark, as I normally would have; The water line was dead-on the 10mL line.

Results?

A difference of 1 drop - 25 PPM of hardness. (10mL via GC = 425 vs. 10mL via "eyeball" = 450).

(((For some reason, my CH shot way up, but that'll be left to another day of troubleshooting! :mad: )))

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Furthermore, I performed the FAS/DPD test twice in the same fashion...one vial filled via the GC and the other by eyeball right on the 10mL mark.

Results?

A difference of 3 drops - 1.5 PPM of FC. (10mL via GC = 18 drops FC + 1 drop CC vs. 10mL via "eyeball" = 21 drops FC + 1/2 drop CC <--- 1/2 drop as the pink was very subtle and a half of a drop probably would have turned it clear.

NOTE: If I were to have filled the vial by "eyeball" a little over the mark as I did before when performing the FAS/DPD test, then the difference would have been 1-2 drops more.


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I don't know what to make of all this! I know I'm splitting hairs, but that's what I do. It's a curse! But like I said previously: it's all relative. Do it the same every time, and you're fine. However, for accuracy and downright ease of consistency, I will continue to fill my vials with the graduated cylinder.
 
GoGrab... your test results/ numbers show the ~15% difference as discussed above. Right on target for the expected difference.

Use the fill method that's most desirable to you and stick with it.

My opinion, a little controversy and skepticism is good. It leads to a healthy discussion about the topic at hand. A forum and principles built upon science should be able to have these discussions without falling apart. That's what the scientific method is all about.
 
Teald024 said:
GoGrab... your test results/ numbers show the ~15% difference as discussed above. Right on target for the expected difference.

Use the fill method that's most desirable to you and stick with it.

My opinion, a little controversy and skepticism is good. It leads to a healthy discussion about the topic at hand. A forum and principles built upon science should be able to have these discussions without falling apart. That's what the scientific method is all about.
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:goodpost:
 
Varkyl said:
The above graphic is confusing precision with consistency (or repeatability). Good article here Whats the difference between accuracy and repeatability?

The definition of precision is accuracy as shown here - Precision | Definition of Precision by Merriam-Webster
The two words are synonyms
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They are not synonyms. Here is a quote from the Webster page you just posted:
Many of us often use precision and accuracy as synonyms, but not scientists and engineers. For them, accuracy describes a particular measurement—that is, how close it is to the truth. But precision describes a measurement system—that is, how good it is at giving the same result every time it measures the same thing. This may be why even nonscientists now often speak of "precision instruments" for measuring, "precision landings" made by airplanes, "precision drilling" for natural gas, and so on.
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Precision and repeatability are much more related than precision and accuracy.
 

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