Understanding Nitrate monitor

gdemos · Jan 2, 2015

I just bought an American marine nitrate monitor
Aside from having trouble calibrating the high end (10-100ppm); (I keep getting error probe message after the 100ppm calibration fluid); and I have soaked this new probe in the 10 and 100 fluid for an hour each... I am not sure I understand the conversion here...

The monitor as I understand reads NO3-N, not NO3 which we are accustomed to. I found this post online, but I'm confused because my frag tank shows undetectable NO3 on salifert, yet a '6' on the monitor( low setting). Following this calc the monitor would suggest I'm north of 24ppm NO3?? (6*4.4268)

Interconverting Nitrate as Nitrate (Nitrate-NO3) and Nitrate as Nitrogen (Nitrate-N)
The atomic weight of nitrogen is 14.0067 and the molar mass of nitrate anion (NO3-) is 62.0049 g/mole
Therefore, to convert Nitrate-NO3 (mg/L) to Nitrate-N (mg/L):
Nitrate-N (mg/L) = 0.2259 x Nitrate-NO3 (mg/L)
And to convert Nitrate-N (mg/L) to Nitrate-NO3 (mg/L):
Nitrate-NO3 (mg/L) = 4.4268 x Nitrate-N (mg/L)

Do I have to successfully calibrate the high end to get an accurate reading on the low end setting?

Thanks. Greg

gdemos · Jan 2, 2015

And mg/L equates to ppm?

Randy Holmes-Farley · Jan 3, 2015

Yes, mg/L is about the same as ppm, and you do multiply nitrate-N by 4.43 to get to ppm nitrate ion.

I would only calibrate the low end if the nitrate-N reading is less than 10. The value you get should, optimally, be between the two concentrations that you calibrated with.

gdemos · Jan 15, 2015

Lou ended up sending me a probe and I got it calibrated accurately. Very surprised with readings however. Hardly a slightest touch of pink on salifert (call it 1ppm) and 57.5ppm (13 NO3-N) on monitor? With all do respect to AM he won't comment on colorimetric but certainly regards the monitors effectiveness. Are the two different methods of testing actually testing the same thing?