# Accurate method of mesuring nitrates



## mr. luke (8 Aug 2014)

I know the forum belief is that your average nitrate test kit is highly inacurate so i was just wandering what an accurate method of measuring would be?
Im not concerned about nitrates, more of a curiosity


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## ceg4048 (8 Aug 2014)

Get your wallet out and click the link in this post => http://ukaps.org/forum/threads/ferts-causing-high-nitrate.16092/#post-167069

Cheers,


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## mr. luke (8 Aug 2014)

I dont think my wife would be supportive of that product, let alone my wallet 
I may do an experiment where i add a known quantity of nitrate to distilled water and test results with your average test kit.

The reason for this thread is that i was sceptical about your beliefs but i have now converted. 
The reason for my conversion is that i tested nitrite and nitrate on a 12l aquarium that i am maturing as a shrimp setup.
I tested the day before yesterday and the 'results' where,
Nitrite 10+
Nitrate 500+

Yesterday the results where
Nitrite 0
Nitrate 40

Now they are 
Nitrite 0
Nitrate 5

I know this is an impossible situation as the breakdown of 10+ ppm of nitrite would equate to a much higher nitrate reading than 5 if they worked. Also the tank only contains substrate (that leeches ammonia), hardscape and terrestrial mosses on slate chips as an experiment. There is nothing growing in there aside from 2 5cm slate chips of moss but growing is a strong word. There is no way to expell 500ppm nitrate from water with essentially no means of biological removal in the tank.

I believe that the actual cause of nitrate related issues in your average aquaria is the general poor health of the aquarium which people relate to nitrate build up.


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## Sacha (8 Aug 2014)

A nitrate test kit is a good 3- point guide. 

Yellow = low 
Orange = moderate
Red = high 


And ignore the numbers.


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## ceg4048 (8 Aug 2014)

Cheers,


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## GlassWalker (8 Aug 2014)

Which test kit was used to get those results? I don't think I've ever seen one that can measure 500+ unless you use dilution? For sure, if you have a system that can reduce 500ppm of nitrate in a couple of days, I know a lot of unplantable aquaria keepers that would bite your arm off for it!

A low cost way to accurately measure nitrate has been a goal in the past. I decided to build and calibrate my own colorimeter based on the API master test kit. I chose that kit purely as it was by far the cheapest per-test of the ones I've seen out there. The nitrate test on that is notoriously difficult to read. You have to interpret subtle changes in yellows-oranges-reds and it doesn't help the supplied card doesn't match what you see in the tube. Also this test has a known weakness that inadequate shaking of bottle #2 will result in an under-reading. The instructions say 30 seconds, but it was later clarified that was only good for a weekly routine. If left alone longer, additional shaking time may be needed to free up the precipitate in the bottle that does the chemical work.

Anyway, I never did finish that project. I got as far as proof of concept, where I can take a raw reading. I made some rough dilutions of nitrate solution to calibrate, and it worked. I'm not going to over-state accuracy here, but I think I'd be good for better than 20%. Before you think that is bad, bare in mind with the colour card, you could be a factor of 2x out, or possibly more. I'm not going to offer fractions of a % accuracy, nor do I think this is needed. A ball park value may still be useful. And even if this is regarded as unnecessary in a planted freshwater aquarium, I could also use it (with separate calibration) on saltwater too.


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## Sacha (8 Aug 2014)

I find that you need to smash bottle #2 as hard as you can repeatedly on a hard surface in order to release the metallic reagent inside


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## dw1305 (8 Aug 2014)

Hi all, 





mr. luke said:


> I know the forum belief is that your average nitrate test kit is highly inacurate so i was just wandering what an accurate method of measuring would be?


 Nitrates are quite tricky to measure by traditional methods, even with lab. scale analytical equipment. This is mainly because nearly all nitrate salts are soluble, and most chemical methods are reliant on producing coloured compounds that you can measure by colorimetry/spectrophotometry.

A more accurate method (in approximate order of accuracy) would either be Ion Chromatography, ISE (ion selective electrode), Kjeldahl (after reduction with "Deverda's alloy") or a spectraphotometry/colormetric method using cadmium reduction and absorbance at 543nm (this is the "red" colour).

Water companies etc can measure NO3 fairly accurately using Ion Chromatography (IC), but even this isn't entirely straight forward because of the presence of other anions,  and you may need to change columns and your active phase to get repeatable results. The better test kits use semi-quantitative colormetric methods, but you can still get anomalous results.

We got a HPLC and a GC, but we use nitrate ion selective electrodes for most day to day lab. and project work on soil extracts, water etc., but you could easily spend 1/2 a day doing ~10 samples.  People want a simple dip test they can use with their tank water and get a meaningful reading, but there really isn't one.

Even though some of the tanks are actually in the teaching labs., I almost never test any of the water. I occasionally dip the conductivity meter in, as it is the only meter or test that you can use like that and get an accurate result (although not a particularly useful one), and we use the tanks (during the photoperiod) to test whether the membranes on the dissolved oxygen meters are damaged. 

If any-one wants to have a look at the ISE methodology it is here: <http://www.coleparmer.co.uk/Assets/manual_pdfs/27502-12Nitratereplaceable.pdf>. Approximate costs are, the meter would be from about £500 (you could also use it for pH measurement with a pH electrode) and the Nitrate Ion Selective electrode from about £200.

cheers Darrel


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## mr. luke (8 Aug 2014)

It was test strips as my nitrate was off the scale on my api kit and these wnet higher


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## GlassWalker (8 Aug 2014)

I did a test for fun before, making solutions of nitrate at 100, 1000, 10000ppm just to see what the API kit did. Short conclusion was, after a point it doesn't get any more red. So it isn't useful at higher levels as the changes are practically undetectable by eye.

Dip tests are considered even worse than liquid ones. For some consistency, you could have tried a diluted test to bring the sample into the range of the API kit. Of course you need to dilute it with a known nitrate-free source of water such as deionised water.


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