So this has been really bugging me - ie the non reduction of nitrate readings despite pwc
(discussed in another post), so I did a little experiment last night.
Using Tetra test kit for NO-3.
A. Following the instructions to the absolute letter, added reagent 1, reagent 2, added zinc powder and shook for 20 seconds, added reagent 3 - let it stand for 10 minutes.
Result = 25ppm
Observations - it was clear that the zinc powder had not fully dispersed within the reagents during the 20 seconds of shaking.
B. Following the instructions as above BUT after adding the zinc powder I deviated and shook the tube until my arm fell off and the zinc powder was fully disolved 1.5 minutes in total, then continued as per test instructions.
Result = <12.5ppm (closer to zero than 12.5ppm)
Observation - The zinc powder was fully dispersed in this test - as intended by the test manufacturer.
I cant be sure what is responsible for the change in result
1. Full dispersal of zinc powder or
2. Increased time between commencement of test and test result reading (an additional 1 minute and 10 seconds)
but....... I suspect that failure of the zinc powder to fully enter solution may be giving a false positive result in nitrate testing.
I have emailed tetra to ask more details of just what is in there tests and what effect the above test observations might make on the results, will let you know if they respond.
Really interested to hear anyone elses view.