How to do a correct CYA test

[a3po911]

I’m struggling to balance my pool water. I performed a SLAM for almost a week and passed the OCLT, the water still won’t hold chlorine under sunlight, but looks clear and crystal.

This made me question my CYA level again. Both Leslie's test and my own showed a reading of around 50 before, and all tests were conducted indoors.

Today, I decided to compare indoor vs. outdoor CYA test results and discovered a significant difference:

Picture #1: Indoor Test – The black dot disappeared when the solution level was slightly below 50 (around 47-48).

Picture #2: Outdoor Test – When I took the same tube outside under direct sunlight, the black dot became visible again.

Picture #3: Outdoor Test - I continued adding the solution until the black dot disappeared again, and this time, the reading was slightly below 30.

Base on this situation, do I need to add more CYA?

30000 Gallon, pH: 7.5, TA 125, CH 270, Salt: 3400, Water Temp: 73F

Appreciate any idea.

 

[ajw22]

Use a standard solution to confirm your testing methods…

R-7065 CYA Standard 50ppm (2oz)

tftestkits.net

With a SWG I would take the 30 ppm and add more CYA.

 

[ajw22]

CYA - Cyanuric Acid Test

Cyanuric acid (CYA) is the chemical name for the product commonly called “pool water stabilizer” … Read more…

www.troublefreepool.com

5. Stand outdoors with your back to the sun and hold your CYA view tube at waist level (see notes). Partially cloudy weather is fine. If weather is very overcast or dark, find the brightest artificial light you can.

Notes:

• We recommend strong indirect lighting, with the sun to your back. Very roughly speaking, direct overhead sunlight is around 100,000 lux, strong indirect light (i.e. shaded from the sun) is around 10,000 lux, an overcast sky is around 1000-5000 lux but varies on how overcast (which is why a bright white cloud overcast is still OK), indoors is usually < 1000 even in a bright kitchen (more typically 500 lux). Sunlight, even on an overcast day, will provide more accurate results than indoor lighting.

CYA Testing - Further Reading

www.troublefreepool.com

Light Conditions Matter For Reading the Dot​

As much as possible, you should do the CYA test in the same consistent light conditions:

• Outside in full sun or use the brightest indirect indoor light that you can if you have to test at night
• Back to the sun
• Don't stare at the dot as you pour
• Fill to a line, hold the tube waist high, and glance at the dot
• If you see the dot, fill to the next line and glance at the dot
• When the dot disappears, you round up the previous line. If you saw the dot at 40 and not at 30, then you call it 40

After reading, you can pour the mixture back into the mixing bottle and try it again; repeated readings on the same sample will give you confidence in the result.

 

[Bperry]

I’m struggling to balance my pool water. I performed a SLAM for almost a week and passed the OCLT, the water still won’t hold chlorine under sunlight, but looks clear and crystal.

This made me question my CYA level again. Both Leslie's test and my own showed a reading of around 50 before, and all tests were conducted indoors.

Today, I decided to compare indoor vs. outdoor CYA test results and discovered a significant difference:

Picture #1: Indoor Test – The black dot disappeared when the solution level was slightly below 50 (around 47-48).

Picture #2: Outdoor Test – When I took the same tube outside under direct sunlight, the black dot became visible again.

Picture #3: Outdoor Test - I continued adding the solution until the black dot disappeared again, and this time, the reading was slightly below 30.

Base on this situation, do I need to add more CYA?

30000 Gallon, pH: 7.5, TA 125, CH 270, Salt: 3400, Water Temp: 73F

Appreciate any idea.



View attachment 629182View attachment 629181View attachment 629180

I was gonna say make sure your water temp is about 70° at least for the CYA test

 

[a3po911]

I added 5 lbs CYA raising 15ppm to see if it can hold chlorine tomorrow.