Taylor K2006 vs. test strip results

So I have been learning alot here and have been convinced that your collective advice is the best advice to follow. My local Leslie's still insists that FC/CYA ratios are crap. Here are my latest test results and treatment method
FC= 10.0
CC = 0
Ph = 7.6
TA = 110
CH = 170
CYA = 70 - 80
Test done in am after adding chlorine the night before. I am in the process of measuring chlorine loss on a typical day and on a typical night
Because I want to raise CH I am temporarily using Cal-Hypo.

Here's my question. I use test strips (I know!) between tests with my Taylor kit to monitor FC. While the Taylor kit reads 10.0 the strips read 3. I know the Taylor test "unbinds" the chlorine attached to CYA which is then part of the result. I assume that test strips do NOT "unbind" chlorine attached to CYA and that (in addition to their inherent inaccuracy) is the reason for the different readings. Or am I off base?

Just subscribed. Its cheap compared to the savings resulting from great advice. Sorry, we don't own a landline.

leslies is full of crap IMO. there is a direct relationship between CYA and FC.

the best guess chlorine guide should be kept top secret and charged for! that best guess chlorine chart is one of the best bits of info on the web for a pool owner.

my first year of pool ownership was great, second year was full of problems, mainly algae and leslies had me convinced I needed one of everything they had on their shelves to get rid of it. I wish I had the money back that I spent on phosphate remover alone at almost 30.00 a bottle! I got tired of spending 60.00 or more every other week at the pool store, that's when I found this site and spent the money on a taylor kit.

once I got my taylor kit these folks helped me get my pool clean and I have been algae free for over a year and I run my pool for about 30.00 a month all summer long and about 15.00 to 20.00 during winter here in central FL. it was almost a full year before I stepped back into a pool store, and only recently went back in for two bags of chlor brite so I could shock and add some CYA to my water. I only shock my pool about once a month ( with bleach ) just to polish up the water and get back that extra sparkle.

your numbers look good and that CYA of 70-80 is good for central FL, I run around 80-90 and only add bleach to my pool every few days. I lose any where from 1-2 PPM FC a day, tops 3PPM FC with a heavy bather load ( kids )

I cant help with your test strip questions but just wanted to chime in since I read central FL/leslies/CYA 70-80 in your thread....

Quote:

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Originally Posted by nefretrameses

... the Taylor kit reads 10.0 the strips read 3.

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Thanks for demonstrating the unreliability of the strips. I can't explain why the strips are inaccurate but why even try? You know and have proved the strips can't be trusted.

Well I was hoping that they would at least be CONSISTENTLY inaccurate. That way I could use them to monitor relative levels throughout the day.

Quote:

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Originally Posted by nefretrameses

My local Leslie's still insists that FC/CYA ratios are crap. Here are my latest test results and treatment method
:
Here's my question. I use test strips (I know!) between tests with my Taylor kit to monitor FC. While the Taylor kit reads 10.0 the strips read 3. I know the Taylor test "unbinds" the chlorine attached to CYA which is then part of the result. I assume that test strips do NOT "unbind" chlorine attached to CYA and that (in addition to their inherent inaccuracy) is the reason for the different readings. Or am I off base?

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No, the test strips are inaccurate because simply exposing a chemical to the water to indicate concentration is tricky since it relies on diffusion/circulation and approximate amounts of water pulled out and onto the test strip, among other factors. The drop-based kits rely on precise stoichiometry for chemical reactions.

The FC/CYA ratio is not crap. It's science and proven in tens of thousands of pools. Print out and give the Leslie's person this scientific peer-reviewed paper and if they still can't figure it out then print out and show them this post and if they still can't figure it out then print out and show them the "Chlorine/CYA Relationship" section of this post and if they still don't understand it, well, give up.

Thanks for the references. I read them thoroughly and understood for the most part. Although my background is in engineering it appears to come down to basic chemistry.
I assume that the reason you mentioned for test strip inaccuracies are what I meant by "inherent inaccuracy". In addition, it does not appear that there is a release of bound chlorine when using test strips like there is in a drop based test. (Can you confirm for my own understanding?) If test strips do release bound chlorine I would really see how bad they are.
I wouldn't consider trying to convince Leslie's. I have enough to do without adding that head banging experience. I tried twice and basically got: "The people on the Internet are not dealing with pools in Florida. Pools in Florida are different." So I go when I need something I can't get elsewhere and leave them to their corporate ignorance
Interesting that FC/CYA relationship is "old and well known" (for 40 years), yet it is largely unrecognized in the industry.

Yes, it's just chemical equilibrium such as taught in 1st year college chemistry or in high school. The difficulty is that there are 13 simultaneous chemical equilibria among the chlorine bound to CYA, the protonated CYA variants, and hypochlorous acid / hypochlorite ion though I use these to calculate the active chlorine (hypochlorous acid) concentration in this spreadsheet and I derive the FC/CYA ratio approximation in this post.

As for the rate at which chlorine releases from CYA when hypochlorous acid is used/consumed, it is very fast where half the FC gets released in 0.25 seconds and this happens regardless of the type of wet-based chemical test (i.e. test strips, OTO, DPD, FAS-DPD) so your assumption is incorrect. Test strips are just pre-packaged wet-chemistry methods -- it is still chlorine reacting with a dye that is adhered to fibers in the test pad, though a different indicator dye is typically used. The methods all work by redox where chlorine oxidizes the indicator dye to a different colored form. The intensity of color is proportional to the quantity of chlorine, so is clearly dependent on how long you keep the strip dipped into the water and on how big a drop you get when you pull the strip out and let it continue to react. The size of that drop will not only be related to how quickly you remove the strip from the water, but to the surface tension of the water itself.

It is only methods that measure instantaneous chemical quantities that correlate with the active chlorine level, such as ORP, amperometric techniques, and membrane chemical-specific sensors. Test strips are also affected by temperature (I forgot to mention that part) because you do the measurement after a certain amount of time but reaction rates are temperature dependent.

If there had been no release of bound chlorine, then when CYA is present you would not have measured any chlorine with the test strips because when the FC is around 10% of the CYA level, the active chlorine level is the same as when there is only 0.1 ppm FC with no CYA. So it wouldn't show up.

Now, that said, the chlorine test strips tend to be one of the better ones. The CYA test strips tend to be one of the worst. Usually you only see Total Hardness strips and not Calcium Hardness so they are measuring magnesium in addition to calcium. Total Alkalinity is also so-so -- usually better than CYA, but often worse than the chlorine tests. And of course, the resolution for these tests isn't very good since they are generally visual "compare to a standard" tests. The FAS-DPD chlorine test, on the other hand, is a "count the drops" test that has a resolution of 0.5 ppm when using a 10 ml sample and 0.2 ppm when using a 25 ml sample. The test accuracy is within one drop or 10%, whichever is greater, and that's a conservative accuracy range -- you can usually do better to within 5% if you are careful.