How to read phosphates?

[paola1315]

Hi all!
I'm not sure how to read the phosphates test. Is NT-labs test, they don't exactly explain whether the bottle should be placed on the paper or just compared to the color up close. I ask this because the color changes completely depending on how I read it. It darkens a lot if I put it down. Does anyone have any experience with these tests? Unfortunately I can't find instructions online

 

[Reef_at_Sea]

Those tests are very difficult for phosphates, i recommend getting a hanna tester.
They are expensive but phosphate is a important parameter.