Picking a "baseline" test kit

[jleonard]

Has anyone compared results from different test kits with those from a pool store? If so, which do you choose as your "ground truth"?

I have used several test kits at home (ColorQ, Pentair78DPD) and at a local pool store (BioGuard/Alex) with pool samples drawn at the same time and under the same conditions, and gotten different results from each test. The results were different enough that when I crunch the numbers to determine amounts of chemicals to add to the pool, one kit would suggest I add 1/2 bottle of acid, while the other suggested I needed 4# of baking soda.

With the ColorQ, I emailed tech-support at LaMotte, and received much of the same advice with respect to the wait times between adding the drops and taking the readings, and with the temp of the water. I adjusted my testing protocol (to the point that the coolness-factor of the ColorQ was greatly minimized), and still got different results.

SO - I'm still on the market for a test kit I can use at home that will produce results consistent with those I get from the pool store. Of course, the pool store could be out-of-calibration, so I plan to compare different pool stores in the next few weeks.

Has anyone compared the TF-100 with a professional system (like BioGuard/Alex?) What do you as your baseline?

Thanks in advance for your advice and suggestions!

John

 

[duraleigh]

Hi, John,

Welcome to the forum. I have a dog in the fight so I will let others answer your very good questions. There's lot's of past discussions on and around this same topic so it won't be long 'til you get some interesting responses.

 

[JasonLion]

Welcome to TFP!

There are several things to keep in mind when comparing test kits. Different tests have different levels of precision and different conditions under which they achieve that level of precision. For example the ColorQ can be remarkably precise (ideally +-0.01) at measuring PH but only when the FC is within it's design range (0-10). By comparison the Taylor PH test is noticeably less precise (+-0.1) but retains that precision over a somewhat larger range, FC 0-15. When making comparisons it is important to keep the precision in mind, since different test results can still be within the precision of the tests and so are really equivalent. Test strips have particularly low precision, even when read by fancy colorimeters.

Second, the tests must be performed correctly for the results to be correct. Many pool stores employ people who are not properly trained in performing the tests. Many people report getting wildly different results depending on which person at the store helps them or which store they go to even when everyone is using the same test kits.

The Taylor chemistry seems to be the most reliable in practice. Taylor chemistry is used by TF Test Kits in the TF100, which is what many of us here recommend. The very best of the fancy machines used by pool stores can achieve slightly better results in some situations but only when operated by a properly trained person who takes the time to actually follow the correct procedures. And some of the "fancy" machines used at pool store are way way worse than Taylor chemistry.

Another thing to keep in mind is that high precision is not what is really needed. The important thing is to use a test procedure that produces reasonably consistent results that is convenient enough that you will actually use it. It doesn't really mater if the PH is 7.4 or 7.42 or 7.5 or even 7.6, everything will still be fine. While there are some great pool stores out there, many pool stores tend to give wildly varying results.

 

[Guest]

I test water at work and use both LaMotte and Taylor. I would use Taylor as a baseline and NOTHIHG is going to give the same results as ALEX, which was designed to sell chemicals to unsuspecting victims.

I have usued standards to check different kits and strips and I always go back to Taylor for home use!
At work we use the LaMotte Waterlink Express (a $1000 colorimeter) with LaMotte UDV's and I STILL backup certain tests with titrations because of limitation to the colormetric tests (for example, calcium hardness will read low when the test approaces or exceded the limit of the meter--not much good for those customers with CH avove about 450 ppm and I have several with well water that exceed that by quite a bit!). Also, the LaMotte TA tests will bleach out if FC is much above 3 ppm. I have spoken to LaMotte about these limitations and their advice was to titrate on these tests!
Be aware that other companies beside Taylor offer titration tests. These are also available from LaMotte and Hach. However, the Taylor are readily available and have a proven track record.

BTW, the main reason stores use systems like ALEX or Waterlink is to speed up testing. When summer comes I usually have people lined up about 6 deep for water testing all day, every day with 2 of us testing! If I were using a Taylor lab the wait time would increase tremendously! I can run a battery of tests including metals in under 5 minutes a person with the Waterlink. The trick is KNOWING when I need to back up a test with a titration.

 

[Butterfly]

SO - I'm still on the market for a test kit I can use at home that will produce results consistent with those I get from the pool store.
John

Welcome to TFP, John :-D

......you actually want a kit that will produce results consistent with results from the pool store? I know I am a relative newbie, but that is the one thing I try to AVOID! The only time I would trust a pool store water test is if Waterbear did the test for me. The most highly touted kit around here is the TF Kit sold on this site by duraleigh. It has a link on the homepage and in lots of sigs. No need to go to the pool store to have water tested. We trust our own testing.

Good luck.


Joyce

 

[dschlic1]

As for the LaMotte ColorQ you might want to get a hold of LaMotte tech support. They received some substandard parts that affected the calibration of these units. The repair should be covered under warranty.

 

[JCJR]

Has anyone compared results from different test kits with those from a pool store? If so, which do you choose as your "ground truth"?

John

I have the Taylor kit and have compared it to the pools store as stated in your question. Three different pool stores use Taylor as well and their results are inconsistent from my readings. I've even took two identical water samples ( I added two drops of CL on one to throw off the tester in case he caught on) and TA, CH, PH and CYA were off 40ppm, 100ppm, .4 and 30 ppm respectively. I did this to prove a point to my cousin who always goes to a pool store.

Also keep in mind that the water sample changes its chemistry from the time you take the sample and arrive to the pool store. In my case it is from 10 min - 20 min difference.

I have taken readings one after another with my Taylor kit and have gotten the exact result so I know it is consistent as well as testing a couple of hours later with very little change.

I guess the most important thing is that I take my time and measure correctly, which produces good results. The pool guys usually turn on the mixer and add water to the beaker. How can they get the proper ml sample with the water swirling? And they also squeeze the regeant bottles and do not get full drops, more like a stream. They sure are in a hurry and don't measure correctly.