Muriatic Acid Effect on CYA Test?

[Jaywalker]

Sorry if it's mentioned elsewhere - search doesn't seem to be working for me today.

Does adding muriatic acid effect the reading of the cyanuric acid test?

I just drained 80-90% of our pool in order to get rid of our 120 CYA reading. On refilling I ran through the standard tests with the following results:

FC=1
CC=0
pH=7.8
TA=170
+Added 48 oz 6% bleach at this point.
CYA = 0
CH=240

As the CYA was the reason for the drain, and we didn't drain the whole thing, I would have expected a CYA reading of 16 to 32. When I didn't get it, I wondered if I had clobbered the test by adding muriatic acid immediately prior. Comments?

 

[257WbyMag]

I don't think that adding MA would really affect the CYA reading, given that you allowed the water to circulate for at least 30 minutes after adding it.

Since you drained off nearly all of your pool water, the amount of CYA in there may be fairly close to nondetectable now. I probably would have drained no more than half your pool. If it is full now, go ahead and recheck the CYA once more and then add enough CYA to get you to 40 ppm.

 

[Jaywalker]

Thanks, 25-06 Improved. I did not wait 30 minutes before measuring CYA after adding MA, but I checked again 3 hours later and there's still no trace of CYA. It's mystifying - there should be a measurable amount. The last time I drained about a third, and my CYA level dropped by the same fraction.

Since I didn't expect to need to add CYA - ever - I don't have any conditioner. Instead, I loaded the feeder with 3-inch chlorine/CYA tablets and broadcast some Leslie's granular powder chlorine. I'd really hate to have to buy CYA...

 

[frustratedpoolmom]

Is the granular Dichlor? Cal-hypo?

 

[257WbyMag]

Thanks, 25-06 Improved.

:lol: Now that is funny! Got me laughing and I can't type because of it.

Anyhoo, yeah, what FPM said...if the granular you're adding is dichlor, it's got CYA in it so keep in mind that it will raise your CYA. If it's cal-hypo, it doesn't have CYA.

 

[Jaywalker]

Granular is dichlor, tabs are trichlor, so I am adding CYA, slowly.

 

[257WbyMag]

Alrighty then. To note though, the trichlor is adding CYA slowly, but the dichlor is adding it really quickly. Keep track of it.

 

[Jaywalker]

Will do - thanks.

 

[PaulR]

It's mystifying - there should be a measurable amount.

If CYA was 120 and you drained 80-90%, there would be 10-20% of the original CYA left, or 12-24ppm (not 16-32). At the low end that could easily be undetectable (very minimal clouding in the view tube).
--paulr