CYA Testing

[Glassonion]

Hi all.
Thanks for all the awesome info on the site. I'm just getting my feet wet with my new AG pool. Everything going fairly well so far.

I have a question about the CYA test. I believe it is a turbidity test based on generating some precipitate in the test. Does anyone know whether the precipitate affects the refractive index in a known manner?
I happen to have an Abbe refractometer and would be curious if I could be a bit more quantitative than the black dot test with it.

-Marshall

 

[kimkats]

@JoyfulNoise this has your skills written all over it!

 

[JoyfulNoise]

They are crystals of hydrogen bonded melamine cyanurate. They are suspended in the aqueous solution but they don’t really modify the refractive index all that much. One typically uses a nephlometer to measure the change in turbidity which in turn is correlated to the concentration of cyanuric acid. A refractometer will not help.

 

[sbcpool]

I find running the CYA test a little bit backwards helps me more than the standard way. I'll get the solution ready and then just pour it into the viewing tube to the 20 ppm line before checking the visibility of the dot. Then I fill it to 30 and repeat. For me it's easier that way. If it's visible at 20 and not at 30 I'll just treat it as 30.

I add that in case you're wanting to find an easier way to test CYA. If you're just exploring more precision for the fun of it, then by all means.

 

[Glassonion]

@sbcpool - Yep, that makes sense. I was mostly just looking for quantitation for the fun of it. I know I'm somewhere between 20 and 30, so that's good enough for figuring required FC, etc. Many many years of lab work make it hard to accept "good enough" when doing measurements

 

[kimkats]

Once you see the googley eye then call it good! Just don't go looking for it or you will see it looking back at you. Just glance in to see if you can see it.

 

[sean.a.hyde]

They are crystals of hydrogen bonded melamine cyanurate. They are suspended in the aqueous solution but they don’t really modify the refractive index all that much. One typically uses a nephlometer to measure the change in turbidity which in turn is correlated to the concentration of cyanuric acid. A refractometer will not help.

If someone was crazy enough to buy a Nephelometer, how can they relate this to CYA concentration?

 

[JoyfulNoise]

If someone was crazy enough to buy a Nephelometer, how can they relate this to CYA concentration?

You would have to run a series of tests on KNOWN standards of CYA and then plot the scattered light intensity as a function of concentration in order to come up with a calibrated curve for the device (this would have to be done often to ensure device linearity and take into account aging effects of the light source, cuvette and photodetector). Then you would need to measure an untreated pool water sample (zero reference) and then a sample treated with the CYA reagent. You could then compare your pool water sample (minus it’s blank offset) to the calibrated curve.

Sounds like lots of fun for a single parameter test, no??

 

[sean.a.hyde]

You would have to run a series of tests on KNOWN standards of CYA and then plot the scattered light intensity as a function of concentration in order to come up with a calibrated curve for the device (this would have to be done often to ensure device linearity and take into account aging effects of the light source, cuvette and photodetector). Then you would need to measure an untreated pool water sample (zero reference) and then a sample treated with the CYA reagent. You could then compare your pool water sample (minus it’s blank offset) to the calibrated curve.

Sounds like lots of fun for a single parameter test, no??

Darn. I was hoping it was something like "Nephelometer reading of XX == CYA of YY". Oh well. The variability of the CYA test always makes me nervous. I probably have between 50 and 60ppm of CYA. So I probably need between 4 and 9ppm of chlorine... that's a big range. I have an SWCG, but the pool is covered most hours of most days (keeps the heat in and gunk out). I let it air a bit on the days we don't actually go in it for a couple hours, but the chlorine demand is very low.
I was just trying to remove a variable, but oh well

 

[Palpatine]

My head hurts after reading this thread

 

[Jnet]

Yeah, but it's a good hurt, right? That's knowledge swelling your brain.