K-2006 accuracy?

[Hilton]

I am becoming very confused.

Last year, all testing was done using test strips. Not once over the course of the year did I ever get a combined chlorine reading at any of my 16 pools and hot tubs. Independent testing by both our supplier (using a BioGuard test lab) and by the health authority (using a Taylor K-2005) had similar results.

This year, we finally started using K-2006 test kits. Every single day I have CC readings of 0.5-1.0, and often 1.5. At one location, the outdoor and uncovered mini-pool and hot tub consistently read 2.0-3.0! Meanwhile, the pool supplier and health authority get CC readings of 0-0.5. Tests using R-0867 have confirmed little to no leftover MPS in the water.

What is happening? I know the K-2006 is supposed to be more accurate, but the readings should still be in the same ballpark as other tests.

I spoke to Wayne at Taylor directly to confirm I was doing the FC/CC and MPS tests properly. He couldn't come up with any explanations.

Yes, the reagents are relatively fresh, and they have been stored properly since being in my hands.

oing the FC/CC and MPS tests properly. He couldn't come up with any explanations.

Yes, the reagents are relatively fresh, and they have been stored properly since being in my hands.

 

[linen]

When you do the FC test are you going until the last drop showed no change from the previous drop? If you are not, then the CC test may typically read 0.5 high. You do not count the last drop for the FC test in figuring your results. You could try a 25 ml sample test instead of the 10 ml, to see if you still get higher CC, since that method gives 0.2 ppm resolution. I think the Taylor kit has instructions for that.

 

[chem geek]

I don't think it's the MPS because that shows up as CC in the DPD test while it shows up as FC in the FAS-DPD test (not in terms of reacting with dye for color, but in reacting with the FAS-DPD reagent so increases the count of drops).

A 0.5 ppm CC can be hard to see in a DPD visual test, especially if the FC level is higher.

As for the higher readings in the outdoor and uncovered mini-pool and hot tub, that is unusual unless you are measuring during or immediately after high bather load. The 2-3 ppm should be readily discernible on a DPD test, but are those tests being run immediately or are you taking a sample somewhere else? Were the DPD measurements done visually or did they use a photometer? It may just be that you are measuring the current CC but that chlorine continues to react with it over time after you've removed the sample. In the one that measures 2-3 ppm, try taking a sample out of the water, measuring the FC and CC, then rinse thoroughly and take another sample out but this time wait for about as long as it takes to get to the pool supplier (assuming they measured off-site) and see what measurements you then get.

 

[JasonLion]

The FAS-DPD chlorine test is the best one available. I would believe it over any of the other tests you mentioned. There is some chance of doing the test wrong, switching to the CC portion of the test before the sample goes completely clear, but that is easy to learn not to do and otherwise the test is very reliable.