Are tests really accurate?

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C

Crimson

0
May 26, 2009
72
Seminole, FL
New pool owner trying to get his head around all the chemistry of pool ownership. What I am finding frustrating is getting different results from different stores. I've been to 4 different stores trying to get consistent results. Here is what I am getting:

TA - 110, 110, 150, 160
CH - 210, 220, 220, 360
CYA - 35, 40, 40, 60

Are the tests just that inaccurate, is there too much 'human error' in them? Or are they just using bad reagents, etc? I don't get it. Obviously a different between 110 and 160 is important for TA, but I don't know who to trust. The difference between CH is probably minor, but the last store said it was way out of wack. And lastly the CYA test is a heck of lot different between 35 and 60!

Is the only solution to get a test kit myself? But I would like to know if I get one of the kits mentioned here will I get accurate results or are all these tests kind of flawed in some way? Why are the pool stores all over the map?
 
Crimson said:
Are the tests just that inaccurate, is there too much 'human error' in them?
Yes, too much human error. Pool store employees are not always well-trained nor paid very much and are often in a hurry.

Or are they just using bad reagents, etc?
Possible, though human error is more likely or a poorly designed test -- some use test strips; others use drop-based tests

Is the only solution to get a test kit myself?
Yes.

But I would like to know if I get one of the kits mentioned here will I get accurate results or are all these tests kind of flawed in some way?
No. There is some variability between different test kits, but not by as much as you were seeing. The accuracy of most tests is around +/- 10 ppm. We recommend the Taylor kits, specifically either the Taylor K-2006 you can get at a good online price here, the Leslie's Chlorine FAS-DPD Service Test Kit, or the TF100 from tftestkits.net with the latter kit having 36% more volume of reagents so is less expensive per test (test kit are compared here).

Why are the pool stores all over the map?
Because their people are not well-trained and some of the test kits they use are not very good.
Click to expand...

For drop-based test kits, the biggest variability most likely comes from a variability in drop sizes from the dropper tips. Static electricity can also be a factor that is easily mitigated by wiping the dropper tip (see this useful info from Taylor).

Richard
 
The pool store i use to test my water sometimes uses a spectrophotometer/colormetric test. These are pretty accurate if the instument is calibrated properly. They are usualy spot on with my Taylor 2006. Only thing I've found is the TA can varry by 20 ppm.
 
What doesn't make sense though is that they are consistently inconsistent.. :hammer: The stores that come up high are ALWAYS high relative to the others, and the ones that come up low are always low.. I guess I have no choice but to do it myself!!!
 
Crimson said:
I guess I have no choice but to do it myself!!!
Click to expand...

You'll be glad you did. There is a certain satisfaction of taking total control of your pool, not being at their mercy and not being tempted to buy chems they "insist" you need. You aren't pressured into thinking you are doing something wrong. You KNOW you have it right and there is no guesswork anymore. You aren't inconvenienced at all by having to go the pool store, and then tempted into buying something on impulse.
 
Brad S said:
The pool store i use to test my water sometimes uses a spectrophotometer/colormetric test. These are pretty accurate if the instument is calibrated properly. They are usualy spot on with my Taylor 2006. Only thing I've found is the TA can varry by 20 ppm.
Click to expand...
Sounds like you are talking about the LaMotte waterlink system. It has some drawbacks (Used it for a long time and passed LaMotte's waterlink certification). The CH and TA are colormetric and not titrations and therefore are not as acccurate as a titration test. Also, the CH test has some problems with the precision of the test when the CH is near the upper limit of the meter (it reads much lower than it is in this case).

In other words, A good test kit can give you better results! (I often backed up the results from this system with a Taylor kit because of these limitations.)
 
Your right about the TA. thats really the only reading that varys much. My Taylor kit gives me a consistent 70-80ppm. Their system always shows 10-15 ppm lower. I dont wory too much about the CH since i have vinyl. My fill water is very soft so i dont check it much. Last time i checked CH it was around 120. Pool store said 130, so pretty close.
 
Brad S said:
Your right about the TA. thats really the only reading that varys much. My Taylor kit gives me a consistent 70-80ppm. Their system always shows 10-15 ppm lower. I dont wory too much about the CH since i have vinyl. My fill water is very soft so i dont check it much. Last time i checked CH it was around 120. Pool store said 130, so pretty close.
Click to expand...
Their TA test starts reading low when the FC is above 3 ppm. Just a limitation of the test. BTW, calibraton of the unit involves sending it back to LaMotte so most places do not calibrate them unless the meter breaks! There is a way to zero them but most places do not know how to do it since it's not in the operating manual (if the store even READ the manual!)
 

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I agree that some pool stores don't train their employees properly. The last time I went to a pool store, I asked them to do a drop chlorine test. Took a while for the kid to find the test, and then when he started doing the test, I had to walk him through it :shock:
He was also testing my water while talking on the phone. Maybe he was good at multi-tasking but I didn't trust the results at all. I have the TF100 and I'm still learning how to do all the tests accurately, but it's easier than I thought it would be testing my own water, plus I'm very careful doing the measurements, unlike a harried pool store employee.
 
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