different CYA readings. Which one is more accurate?

[nikon5400]

I have two CYA bottles, Leslie's and TF100.
The difference in readings is about 10ppm

Leslie's 35-40
TF100 25-30

(I completely forgot I had the same issue last year, only then the readings were 60 and 40)

My TF1000 is from 2017 (authorized ebay seller) and I believe Leslie's is from the same year. Leslie's is from the same bottle they use to test water.

Which reading is more accurate? What's the shelf life of R0013 and how older product affects the reading?

The reason for my concern - my FC loss during cloudy day is 4-4.5ppm. I add chlorine at night, bringing it up to 6ppm, have 5.5ppm in the morning and 1.5-2ppm at night

Thanks.

P.S. My test kits are kept in TF100 shipping box, with room temperature 60-75 (non air conditioned room, so in the summer it may get slightly above 75)

 

[Richard320]

From the symptoms, I'd say the lower reading is accurate. The only way to be certain is to test a standard solution of known concentration. Shop.

 

[nikon5400]

just curious -

1. What's the shelf life of R0013?
2. How does its age/storage conditions affect the test result?
3. if R0013 was diluted with water, how it'd affect the test result?

Thanks.

 

[Richard320]

The first two answers are here, straight from the manufacturer: Cyanuric Acid Reagent, 16 oz

The third is that it could read low. Because R-0013 is a reactant not an indicator. There is a term in chemistry called "limiting reagent". It's the lowest common denominator, sort of. If you were building water and had eight units of hydrogen but only three of oxygen, you could only get three units of water. Oxygen is the limiting reagent. If you had four of each, you'd only get two water because hydrogen would be the limiting reagent.

Now you have CYA and whatever is in the R-0013. If the CYA is really high and the R-0013 is diluted, you will read low. The R-0013 is the limiting reagent. If there is no CYA or very little, then there might still be enough R-0013 to react properly because the CYA is the limiting reagent You just don't know.

But it doesn't really matter, because your reagents ought to be tossed due to age.

 

[nikon5400]

Thanks Richard.
Avoiding switching bottle caps - I'm guilty of doing that I like the older caps.

I wish there was a manufacture/expiration date on all reagents, maybe it would shed some light on why 2 reagents purchased at the same time and stored at the same place have different readings.
I'll get new R-0013 and retest

By the way, I stopped by Leslie's today and their reading is 50.

 

[nikon5400]

We had rain all day Monday
Tuesday night water got cloudy, overnight loss 3ppm. Wednesday morning can't see bottom drain.
Overnight loss was <1 just a few days ago.
Could rain cause this?
Also I mowed around the pool on Sunday and some grass got into the water. Could that cause chlorine loss?
If not, maybe higher CYA reading was accurate and i didn't have enough chlorine?