CYA testing variability

[MarkHoop]

I am finding that my CYA testing results seem to be variable and am looking for a "best practice" discussion.
I tested my pool on July 31 and got 60ppm
Since then I have added 600g of dry stabilizer (7ppm) and tested at ~ 65ppm
I tested again today and have attached the pics going from 70ppm to 30ppm. These would lead me to believe that my CYA is currently 30-40ppm which can't be. Any best practice suggestions when testing for CYA?

 

[Bperry]

These would lead me to believe that my CYA is currently 30-40ppm which can't be.

Why not?

 

[MarkHoop]

Simply due to the fact that it was 60 -70 a week or so ago with no appreciable rain or reason for it to drop by 1/2

 

[Bperry]

Simply due to the fact that it was 60 -70 a week or so ago with no appreciable rain or reason for it to drop by 1/2

How confident are you the 60-70 is accurate? Is the lighting roughly the same as a week ago?

 

[mknauss]

CYA Testing - Further Reading

www.troublefreepool.com

 

[MarkHoop]

Same spot and same time of day. I am confident about my testing to date and maybe the question should be to determine if there is any logical reason why the CYA would drop so drastically in that time period while no other tests showed the same drop (no dilution due to rain or fill water)?

 

[MarkHoop]

I will repeat the test now

 

[Bperry]

Same spot and same time of day. I am confident about my testing to date and maybe the question should be to determine if there is any logical reason why the CYA would drop so drastically in that time period while no other tests showed the same drop (no dilution due to rain or fill water)?

Theres a +\- 15ppm error tolerance on the test so if your results are within 30ppm of each other its considered normal. Thats one reason we say not to spend effort trying to measure 65 or 68 cause it really doesnt matter that much.

Heat also degrades CYA each month, but not that much.

 

[MarkHoop]

Theres a +\- 15ppm error tolerance on the test so if your results are within 30ppm of each other its considered normal. Thats one reason we say not to spend effort trying to measure 65 or 68 cause it really doesnt matter that much.

Heat also degrades CYA each month, but not that much.

Ok, repeated test and am getting 50-60 which sounds way more reasonable than 30. This season I have added ~ 5500 g of Dry Stabilizer which should give me ~ 70ppm so the numbers considering "some" losses seems at least reasonable. 30 ppm did not!!!

 

[Bperry]

Ok, repeated test and am getting 50-60 which sounds way more reasonable than 30. This season I have added ~ 5500 g of Dry Stabilizer which should give me ~ 70ppm so the numbers considering "some" losses seems at least reasonable. 30 ppm did not!!!

It can also take a couple days for stabilizer to register on the tests.

 

[disjustice]

If you have an mg scale, you can mix up 50mg of stabilizer in 1litre of tap water and that will give you a 50ppm solution to calibrate against. Do a test with your calibration water, filling the test vial exactly to the 50 line and take a pic of what the dot looks like and then do your pool water and compare to the calibration pic.

 

[cwswifty]

If you have an mg scale, you can mix up 50mg of stabilizer in 1litre of tap water and that will give you a 50ppm solution to calibrate against. Do a test with your calibration water, filling the test vial exactly to the 50 line and take a pic of what the dot looks like and then do your pool water and compare to the calibration pic.

Great idea!