Having issues with ultra low phosphorous test

rob safron · Feb 17, 2019

I use the Hanna ultra low phosphorous test and always found it accurate until very recently. Now I’m getting weird high readings when I know it’s close to zero so I restest to confirm. Like today, my first reading was 78 followed by the next 2 tests at 0 and 2. Seems to be an every time I test now the first one is way out. My testing is no different than I do each time. I have also tried repeating the test with the same vial using a new vial of tank water and that comes in as expected. Anyone else have issues like this. Getting tired of having to repeat 2 or 3 times because I can’t trust the first one. Also we’re not talking within normal accuracy. Like today it can be 28 followed by two o’s or 18 followed by a 0 and 3. Could the meter be going bad?

jsker · Feb 17, 2019

rob safron said:
I use the Hanna ultra low phosphorous test and always found it accurate until very recently. Now I’m getting weird high readings when I know it’s close to zero so I restest to confirm. Like today, my first reading was 78 followed by the next 2 tests at 0 and 2. Seems to be an every time I test now the first one is way out. My testing is no different than I do each time. I have also tried repeating the test with the same vial using a new vial of tank water and that comes in as expected. Anyone else have issues like this. Getting tired of having to repeat 2 or 3 times because I can’t trust the first one. Also we’re not talking within normal accuracy. Like today it can be 28 followed by two o’s or 18 followed by a 0 and 3. Could the meter be going bad?

Are you rinsing the cuvettes before testing with either distillers or RO/DI?

rob safron · Feb 17, 2019

So I do rinse the used vial with tap first really well then rinse with RODI and let dry. Before testing I fill and empty twice with tank water. I use a micro fiber cloth to clean before testing. And the times I tried testing the same sample using a new vial of tank water for the zero, I did not reclean and the test came back where it should be.