Hanna Marine Nitrate Checker HI781

[Randy Holmes-Farley Verified Community Expert]

Yes just freshly made saltwater lol

SaltwaterQuairum said that Hanna told them (he said she said?) that the range can be extended to 0-50ppm with dilution

With the exact chloride level, I presume. I think it would be nice to see how sensitive it is to the natural variations folks see in both salinity and salt mix.

 

[nereefpat]

With the exact chloride level, I presume. I think it would be nice to see how sensitive it is to the natural variations folks see in both salinity and salt mix.

If chloride had to be exact, then any colorimeter/spectrophotometer or even color comparison test kit would read different values for nitrate for each salt mix, and also for different salinities using the same salt mix.

I suspect that isn't the case. I suppose that it wouldn't be too hard to prove. You would just need to spike different samples at slightly different salinities and test.

 

[Randy Holmes-Farley Verified Community Expert]

If chloride had to be exact, then any colorimeter/spectrophotometer or even color comparison test kit would read different values for nitrate for each salt mix, and also for different salinities using the same salt mix.

I suspect that isn't the case. I suppose that it wouldn't be too hard to prove. You would just need to spike different samples at slightly different salinities and test.

I think that is exactly why Hanna didn't have such a device in the past. They confirmed this was the reason in a post, IIRC.

 

[BZOFIQ]

Yes just freshly made saltwater lol

SaltwaterQuairum said that Hanna told them (he said she said?) that the range can be extended to 0-50ppm with dilution

Clearly you can easily mix up some saltwater but that water also has to be tested to make sure there are no nitrates in it either.

@Randy Holmes-Farley Am I overthinking it.

 

[piranhaman00]

Clearly you can easily mix up some saltwater but that water also has to be tested to make sure there are no nitrates in it either.

@Randy Holmes-Farley Am I overthinking it.

If you use RODI there should be no nitrates though...

 

[BZOFIQ]

If you use RODI there should be no nitrates though...

Hanna Marine Nitrate Checker HI781

Anyone heard any info on this? Wondering when this might be released. I cant find much information about it. https://www.hannainst.com/marine-nitrate-checker-hi781.html

www.reef2reef.com

 

[piranhaman00]

Hanna Marine Nitrate Checker HI781

Anyone heard any info on this? Wondering when this might be released. I cant find much information about it. https://www.hannainst.com/marine-nitrate-checker-hi781.html

www.reef2reef.com

I dont get it.

 

[nereefpat]

Hanna Marine Nitrate Checker HI781

Anyone heard any info on this? Wondering when this might be released. I cant find much information about it. https://www.hannainst.com/marine-nitrate-checker-hi781.html

www.reef2reef.com

Piranha obviously means RODI + salt mix. There shouldn't be nitrates in that either.

 

[Randy Holmes-Farley Verified Community Expert]

My concern is more with variable chloride levels, not the slim chance of nitrate in RO/DI plus new salt mix.

 

[Dan_P]

With the exact chloride level, I presume. I think it would be nice to see how sensitive it is to the natural variations folks see in both salinity and salt mix.

If the test chemistry was sensitive enough, I wonder if a 50% dilution of the sample with RODI renders salinity variation unimportant. Current hobby tests can detect 0.1-0.2 ppm NO3. So you take a hit on the limit of detection to make a NO3 Checker. I assume the low upper limit is for the same reason the ULR PO4 Checker has a low upper limit.

 

[Randy Holmes-Farley Verified Community Expert]

If the test chemistry was sensitive enough, I wonder if a 50% dilution of the sample with RODI renders salinity variation unimportant. Current hobby tests can detect 0.1-0.2 ppm NO3. So you take a hit on the limit of detection to make a NO3 Checker. I assume the low upper limit is for the same reason the ULR PO4 Checker has a low upper limit.

Maybe. Diluting by half drops the chloride impact by half (that is, half the chloride change), but whatever impact it has is then doubled to get back to the final nitrate value. It isn't clear to me the relationship between twice as big of a chloride variation on the reported nitrate variation.

 

[Dan_P]

Maybe. Diluting by half drops the chloride impact by half (that is, half the chloride change), but whatever impact it has is then doubled to get back to the final nitrate value. It isn't clear to me the relationship between twice as big of a chloride variation on the reported nitrate variation.

Some data to help us ponder.

I proposed what seems like a free lunch, halving the chloride content to reduce the effect of the salinity variation in our systems. Here is what I was thinking, but first some information.

The data in the plot below was generated by diluting 1 mL of aquarium water with 9 mL of a diluent made of various ratios of Instant Ocean and RODI. That gave me solutions with an identical nitrate concentration and varying salinities. The results tell a simple story. The higher the salinity, the lower the measured nitrate concentration (I used Red Sea Pro and measured the color intensity with a LR PO4 Hanna Checker).

This is the chloride effect that can cause nitrate measurement of our marine aquarium water to be off or variable when the salinity is not consistently at 1.026. This happens now but the effect is generally not detected when doing color comparisons to a color chart.

Back to reducing this salinity effect through dilution with RODI. I am using the regression line below for the example data.

When a NO3 measurement is made on my aquarium water with a specific gravity of 1.026, the expected NO3 amount is 0.52 ppm (I calibrated my test that way) but it will be 0.59 ppm if the spg is 1.020, a difference of 0.07 ppm or a relative difference of 14%. When I dilute the aquarium water with RODI to a spg of 1.013 (I am diluting 1 mL of tank water with a 9 mL mixture of Instant Ocean and RODI), and retest, if the original spg was 1.026 I measure 0.68 ppm but obtain 0.71 ppm if the original spg was 1.020, a difference of 0.04 ppm or relative difference of 5%. Something for nothing? No. If the color intensity in this test did not increase at lower salinities, the relative difference would not have changed from 14% at the lower salinity.

This approach comes with a cost though. Measuring pale colors means a lower signal to noise ratio and limits how high the nitrate can be measured.

 

[Randy Holmes-Farley Verified Community Expert]

I'm having trouble working through what you did in relation to the math, but in theory I cannot see how this works out if the error is linear with specific gravity.

If you drop the sg by half, in a linear relationship you get half the error, but when you multiply the value back up to the real sg, the error is multiplied too , exactly offsetting the gain.

 

[Dan_P]

I'm having trouble working through what you did in relation to the math, but in theory I cannot see how this works out if the error is linear with specific gravity.

If you drop the sg by half, in a linear relationship you get half the error, but when you multiply the value back up to the real sg, the error is multiplied too , exactly offsetting the gain.

The gain occurs because the signal is not halved. Less salinity means a deeper color and therefore the relative difference is smaller. Without an improved signal strength at lower salinity, the relative error from salinity variation is the same as you point out.

I don’t know how to determine whether the benefit of reducing salinity variation is cancelled by the increased noise in measuring a more dilute solution. I think that depends on the photometer, right?

Are we making progress or going in circles in this discussion?