Hanna PO3 inconsistent?

[Cwentz758]

Hello all I test my tank weekly and my PO3 has been all over started at .13ppm then week after .24 then .09 and today .02.... after the .02 I re-tested 3 times getting 3 different results. (.20 .18 .16). Kinda scratching my head here as to why it’s always different, and should I be thinking it’s somewhere between .16-20 or should I go off the first reading.

the only thing different with the tests.

test 1: used same test tube to zero then added reagent and got .02

test 2&3: used a clean test tube with tank water to zero then used other tube with already tested reagent in it and got .20 and .18

test 4: same as test 2&3 except used the 3 min countdown on the Hanna tester.

thoughts?

 

[Larry L]

You don't say which model of Hanna checker you are using, but those numbers are likely all well within the range of error of the checker. E.g. a reading of 0.18 ppm on the 774 checker could mean the actual value is anywhere from 0.15 ppm to 0.21 ppm, and that's even if your technique is perfectly repeatable.

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

 

[Cwentz758]

Using just the normal low range

 

[elysics]

test 2&3: used a clean test tube with tank water to zero then used other tube with already tested reagent in it and got .20 and .18

You don't want to do that. In fact, you should also make sure the same vial goes in with the same orientation before and after adding the reagent (best to always put it with the writing on the vial facing you).

Also polish it with a microfiber cloth after every time you touch it.

Lastly, dont violently shake it, just swirl it and turn it upside down and back every 10 seconds or so, theres a video on hannas official channel "how to use the hi 736" or something. That way you don't get airbubbles.