CYA increasing faster than possible...

[chem geek]

When you are doing the CYA test are you standing with your back to the sun holding the tube in front of you looking down into it? You want strong indirect lighting. If you have the tube directly in the sun, you will read lower than the actual amount while if you read it in indoor lighting (unless very bright indirect) then you will read higher than the actual amount. See this link for some photos of the black dot disappearing. You can get 50 ppm CYA standardized solution if you want to experiment with your testing technique.

[Themadczar]

Ok, I will try the test in indirect daylight... Thanks for that; I was unaware.