Hannah Inaccuracy- Phosphate ULR vs Phosphorous ULR

[fishnugget1]

I have had Phosphorous Hannah tester for years. Always all over the place. This morning did test 2X. First measured 10. Second 22. Which Do I believe?
Also tested using Hannah Phosphate ULR. Showed .06. I had heard Phosphorous was more accurate but I always need to test 2X and average the 2. Usually tests are far apart. Use same amount of water from a syringe so this is not a variable.

Which should I use?

 

[jpas]

Did you test with the ULR Phosphate meter twice?

 

[fishnugget1]

Yes. That is consistent

 

[homer1475]

Wipe the cuvette down before putting in, making sure there is no fingerprints, or salt smudge?

I use the ULR phosphorus, and can get very consistent results with mine(usually within +-3ppt).

 

[fishnugget1]

I do that now

 

[Larry L]

First measured 10. Second 22. Which Do I believe?

Both? That's basically within the accuracy range of the tester. Hanna says the 736 ULR phosphorus meter has an accuracy ±5 ppb ±5% of reading, so a reading of e.g. 16 ppb could mean an actual value anywhere from 10.2 ppb to 21.8 ppb.

http://larryl.emailplus.org/fish/test-kit-calculators.html