Hanna ulr phosphorus test results

[Trooper182]

May be a crazy question. So I noticed when testing with the ulr tester, I follow the directions and press the button to cycle the 3min countdown before the rest is run. When I get the results it shows whatever it tests at ppb. But if I let the sample sit for say ten min and run the test again the result is consistency higher than the first test. I have tried this a few times when testing and each time the number is higher vs the first reading it gives me. And not just a little higher. So what gives?

 

[SchrutesReefs]

As much as I liked my Hanna phosphorus checker at first, I have started checking it against a Nyos phosphate test kit. My Hanna wouldn’t give me the same 2 results EVER, like not even close. And yes, I oriented the bottle the same way and wiped it down with a cloth each and every time. Had it for over 18mo and never matched itself or my LFS.

 

[nereefpat]

May be a crazy question. So I noticed when testing with the ulr tester, I follow the directions and press the button to cycle the 3min countdown before the rest is run. When I get the results it shows whatever it tests at ppb. But if I let the sample sit for say ten min and run the test again the result is consistency higher than the first test. I have tried this a few times when testing and each time the number is higher vs the first reading it gives me. And not just a little higher. So what gives?

Do you mean let the sample sit with the reagent in it? It makes sense that the value would creep up over time if that's the case.

 

[Trooper182]

As much as I liked my Hanna phosphorus checker at first, I have started checking it against a Nyos phosphate test kit. My Hanna wouldn’t give me the same 2 results EVER, like not even close. And yes, I oriented the bottle the same way and wiped it down with a cloth each and every time. Had it for over 18mo and never matched itself or my LFS.

I just don't get how the result can be so wildly different. It always shows low on the first test which is why I tried testing after letting the sample sit for a few min. Doing that the test always showed +- 1 of each other. This is the last test I did. I ran the test with the same sample 3 times after the first one and it stayed +- 1 of this number.

 

[Trooper182]

Do you mean let the sample sit with the reagent in it? It makes sense that the value would creep up over time if that's the case.

Yes, letting it sit after mixing the sample with reagent.

 

[SchrutesReefs]

I just don't get how the result can be so wildly different. It always shows low on the first test which is why I tried testing after letting the sample sit for a few min. Doing that the test always showed +- 1 of each other. This is the last test I did. I ran the test with the same sample 3 times after the first one and it stayed +- 1 of this number.

Agreed. If you ever get it figured out let me know.

 

[gbroadbridge]

May be a crazy question. So I noticed when testing with the ulr tester, I follow the directions and press the button to cycle the 3min countdown before the rest is run. When I get the results it shows whatever it tests at ppb. But if I let the sample sit for say ten min and run the test again the result is consistency higher than the first test. I have tried this a few times when testing and each time the number is higher vs the first reading it gives me. And not just a little higher. So what gives?

I'm not sure what you don't understand.

The reaction is time critical, which is why there are explicit instructions to gently mix for 2 minutes and then wait exactly 3 minutes to read the result.

If you wait any long the reaction will continue and you will get incorrect results.

You can assume any test that contains instructions to read the result after a fixed time period, will give incorrect results if read any later than instructed.

 

[nereefpat]

Yes, letting it sit after mixing the sample with reagent.

To me, this is expected. The phosphorus is reacting with compounds in the packet to display a certain color. The reagent colors the sample in proportion to how much phosphate is in the sample. The reaction is time dependent. All color comparison type tests will behave this way to some extent. The longer they sit, the darker/lighter they will become.

Edit: @gbroadbridge beat me to it, sort of.