Pool store test results vs home test results

[czipper]

I've gotten very used to home tests over the last few years, and with the support available here have had a "troublefree pool". After a liner change I have totally new fill water and have been doing a lot more testing than I've needed to do in the past, and i've used the local pool store for water testing once or twice since I get my 12.5% bleach there anyway. They now have an all electronic system where they inject just a few ml of water into this little plastic disc and all the numbers you want come out in less than a minute or so. The curious thing is that I tested my water at home just before bringing a sample to them, and my results were kind of close to the pool store, but they were not the same.

Which result should be taken as more accurate? My chemicals are pretty fresh, and have been consistent. The last time I used a pool store's test years ago they didn't have this electronic testing system, and it makes testing multiple parameters really easy.

Any opininons on the discrepancy I described, or which to trust more closely?
Thanks

(Ok, pool stores have an interest in telling me I have an imbalance to sell me some chemicals, but I don't fall for their tricknology, and their results aren't really far off of my home results anyway. I want to know if I can feel comfortable using their numbers to save some time occasionally)

 

[Pool_Medic]

Lamotte spin disks are incredibly inaccurate, I know, I’ve used the system. Nothing bests titration if done properly.

 

[Jimrahbe]

C,

You should always trust your own tests... it does not really matter even "if" the pool tests were a little more accurate.. You are looking for trends in your chemical readings, so it is always better to use the same kit for every test.. Your kit...

Thanks,

Jim R.

 

[Teald024]

I want to know if I can feel comfortable using their numbers to save some time occasionally)

How is it a time saver to walk out of the house, get in a car, drive to the pool store, walk in, catch someones attention, wait for the test, wait for the print out, listen to their advice, ignore their advice, drive home, get out of the car, walk back in the house....
Even if you were going out anyway or going to the PS for supplies, it's still quicker to do it yourself.

Use and trust your results of your own kit.

 

[Donldson]

Wanna know what is even more inaccurate than a pool store doing hand testing? A pool store doing electronic testing.

As I said to someone else recently, they don't install those things because they are more accurate but to convey the image of being accurate. It's all just a dog and pony show that, unfortunately, has proven to be quite effective. The number of people who are convinced these things must work great because TECHNOLOGY! appears to be significant...

 

[ajw22]

There is a difference between accuracy and precision. Those electronic tester can be precise with their numbers. That does not mean the results are accurate.

 

[Wobblerlorri]

The trouble with any technology is that it always requires calibration and education to use properly. For a pool store to test water properly in one of these gadgets, they would have to run a known sample before running your sample Every. Single. Time.

Even more important, the person doing the testing has to know the proper technique for using the device. I promise, it's more complex than injecting the sample into the disk and banging it into the machine.

I'd be even more cautious about the accuracy of this test over the colorimetric test we use. Trust your own test results -- there's a reproducibility there you won't find at the pool store.