Inconsistency with Hanna Nitrate HR Tester?

[Ober_Reef]

Hello Everyone,

This is the second weekend in a row where I first pulled zeros on my Hanna Nitrate HR tester and decided to test again and got higher results. Today I went from zero to 2.9 and the time difference was basically the amount of time to run the test. I test after my water change every week and today I waited an hour or so after the change to do the test.

I also do dose Mocrobacter 7 after each water change.

Any ideas ?

 

[blaxsun]

Myself, I'd probably do the water change, wait an hour, test - then dose MicroBacter7.

 

[Idech]

It’s pretty much within it’s accuracy range :

Nitrate Accuracy	±2.0 ppm ±5% of reading

 

[Ober_Reef]

Myself, I'd probably do the water change, wait an hour, test - then dose MicroBacter7.

I was wondering if that could have an effect that’s why I mentioned it.

 

[jpcaram]

It’s pretty much within it’s accuracy range :

Nitrate Accuracy	±2.0 ppm ±5% of reading

I see this confusion a lot. Accuracy does not tell anything about the variation between measurements. Accuracy is an average (of infinite measurements, thus a theoretical value, or of many values such as to approximate the former) of how off-target the measurements are.

So, with the same device, same water, same cuvette, same battery level, etc, etc, on average, your measurement should not average to a value that is off by more than 2ppm from the true value.

Now, with that being said, the "spread" around this "average error", or in other words how far in value we can expect one measurement result from another will only depend on things that changed between values.

So, if you measure 0ppm, then 2.9ppm, it is not due to the instrument. The variation due to the instrument, as I can interpret from the spec is the "+-5% of reading", and we can call that "instrument measurement noise". Unfortunately, Hanna does not clarify this.

 

[BanjoBandito]

They don't do well under 5 from my experience. Of coarse I haven't had under 5 nitrates in many, many moons so....just my opinion.

And yes, accuracy....I've tested water 4 times in a row and gotten between 26 - 30. So I tend to average them out.

DIRECT REEF BEEF QUOTE: "test til you get a number you like then you are done"