Calcium Hardness Testing discrepancy

[Ian196499]

Hi All,

I’m just starting my 2nd season of my refurbished pool. Start up has gone well and the water is sparkling clean and the family is enjoying using it.

Thanks to all the folks on the forum for all the help I’ve got from reading how to do things!

For testing I followed the advice on the forum and got a Taylor test kit. However the reagents are extremely expensive to source here in the U.K. so I purchased a Palintest6 Test kit.

All the tests are very similar between Palintest6 and Taylor ( FC/ CC / pH/ CYA /TA) with the exception of Calcium Hardness.

My current results are :-
FC 1.8
CC 0.2
pH 7.4
CYA 26
TA 102
CH 156 Palintest - 250 Taylor

I found a thread from last September discussing this exact problem but I couldn’t see a solution.

Is anyone else having this issue?

The supplier sent me some new test strips but they seem to give the same results.

Next step will be to return the kit for recalibration but as it’s brand new I doubt that’s the issue.

Thanks for any guidance
Ian

 

[JoyfulNoise]

I suggest you find a supplier of a calcium hardness standard and then retest. The two tests you are comparing use different methods and indicators for calcium hardness detection. The Palintest protocol uses a photometer that is designed to look at a specific wavelength of light which is absorbed by the Calcicol reagent added to the sample water (purple colored solution of different intensities). The Taylor reagents use Eriochrome Black and an EDTA titration method to measure calcium concentration. The only way to know if the test method is working correctly is to test a known standard. In the US, Taylor sells a 250ppm CH standard that is NIST-certified and traceable. I'm not sure what's available across the pond there in the UK but if you can find a supplier of a CH standard that is traceable to a standards lab (like NIST in the US), then you'll know if your tests are working.

 

[Ian196499]

Thanks! I’ll speak to a couple of suppliers and see if that’s something I can get hold of.

 

[JoyfulNoise]

Generally speaking, the two tests have different issues associated with them.

For the Palintest system, you're dealing with a digital photometer and plastic cuvettes. Any aging in the light source, the detector, electronics or the test tube itself, will cause drift in the system and measurements. In a laboratory environment, one would never use those photometers without a specific protocol for calibrating the electronics using standards. Having worked in a chemistry lab, I can tell you that we would calibrate our pH probes daily and sometimes multiple times per day to make sure every measurement was as accurate as possible. For photometer systems, one would always calibrate and zero the system prior to any measurement.

For the Taylor test, the biggest issue would be reagent spoilage and chemical interferences (transition metals like iron and copper) as well as user error. For the most part, the reagents are very stable and so they should last quite a while. User error is always an issue but, with sufficient practice, the errors introduced should get better over time as the user becomes familiar with the test.

I very rarely trust consumer-based photometer testing because the devices used are constructed as cheaply as possible which makes them very suspect. However, here in the US we can get liquid reagents for fairly low cost, so it makes the titration testing method more preferable and easier to fix when an issue pops up.

 

[Ian196499]

Thanks - I appreciate the comments about having the unit recalibrated regularly. I was hoping that it being brand new it would be OK so far but maybe not. The advice I’ve had is that as a domestic unit it should only need calibrating annually. I’ve spoken to the distributor in the meantime and he’s offered to send it back for a calibration test FOC given how new it is.
If I could buy the Taylor reagents here at a reasonable price then I would have stuck with them but Taylor themselves aren’t interested in selling in the UK ( their only outlet is a distributor in Spain) and buying from the US results in a postage cost of 3x the cost of the product and I’m not convinced the shipping process wouldn’t impact the product quality. But maybe someone on the forum knows a better way to source them?
Thanks for the help!
Ian