[Deanna]

Interesting. I've considered trying this, but had concerns about the saltwater aspect and use of zinc. Cadmium tests are easier to do and have more reliable results (mainly because of the shaking requirement for zinc crystals). The API kit uses zinc and the violent shaking required often leads to unreliable/inconsistent results. Apparently, Hanna may have solved this problem. Although the Hanna test still requires the violent shaking, it seems able to ignore any undissolved crystals that may settle to the bottom. I recall @jeffkrol playing around with a DIY nitrate colorimeter and, maybe, Hanna has done it.

If you would be interested in creating additional calibration solutions, I can give you some dilution rates starting from 3L stock solutions, so that you wouldn't need the precision of graduated cylinders.

 

[kjonulak]

Fire away. Is there a way to weigh the water. I have a gram scale that goes to about 5,000 grams.

Also I find that with the 2 minute shake time, I don't see any undissolved crystals in either a SW or FW sample.

 

[Deanna]

If your scale can measure accurately down to about 20g, you can use weight. One ml of water weighs 1 gram.

Below is the dilution table for three ppm targets that I use when calibrating test kits.

 

[kjonulak]

I work on making those solutions and get back with you on the results.

I'll work. Lol spellcheck

 

[kjonulak]

I created the various reference solutions as per your instructions here are the results for the 12/17 and 22ppm concentrations.
Also please note the Hanna HR Nitrate Colorimeter has a +- 2ppm accuracy.

I also created a 2L solution using 0.1 grams of KNO3 which would create a 30.65ppm nitrate solution. Here is what I measured.

For me, I feel that the colorimeter is close enough for what I'm trying to accomplish. Way better than trying to color match a chart.

 

[Deanna]

Well, it’s fairly consistent at 2-3ppm (12-20%) higher than calibration solutions. With my KH and PO4 (low range) Hanna colorimeters, I find that it is useful to take 2-3 readings on the same vial and average the results. This may bring your readings a little close to the expected readings. It may be that the higher readings are due to the test being calibrated to saltwater. You could ask Hanna to comment on that. If you do, let us know what they say.

In any case, the consistency is encouraging in that it seems that you can assume that the correct level is always 2-3ppm lower than the test results, which, as you say, is far better than the color interpretations we usually have to do on the typical tests. You might even try diluting the samples with about 15% RO/distilled water to see if that brings results closer to expected readings.

Thanks for doing the work. When I run out of my current stock of NO3 kits, I will probably buy this test kit.

 

[kjonulak]

With the +- 2ppm if you get one it could be in the other direction. Honestly it is so much easier than using the color matching charts. I can live with the slight error. I have found when I dose the my SW tanks with KNO3 to raise the level it matches to what I dose.

 

[Deanna]

I agree on the value of using it vs. non-colorimeter test kits. Since your SW readings seem slightly more accurate, have you tried creating calibration solutions using your SW mix instead of the RO/distilled water? If you were to find that such a SW calibration solution resulted in expected readings, then this would point to an adjustment made by Hanna, for SW, and we could now factor that difference in to the FW readings with confidence. You could use the same calibration formulas, just replacing the RO water with your SW mix.

 

[kjonulak]

I won't have time to redo the entire experiment again. What I will do is take 3L of SW from my storage tank and test the level of nitrate. I can then add 0.3 grams of KNO3, which will raise the nitrate level by around 61ppm and retest to see the result. I should be able to do this later today or tomorrow. I'll post the results.

 

[Anon]

Hi Folks,

Thanks to @Deanna, I have just quickly scanned this thread. Needless to say, I'll be back again tomorrow!

Anon

 

[cloozoe]

many thanks for this post, kjonulak. Bought the checker (I use and like the phosphate and iron checkers) solely due to your persuasive testing & recommendation.

received it today and prior to trying it tested nitrates with my salifert kit, which I've been using for a long time.

my interpretation of salifert reading was pretty much spot-on 5ppm; perhaps a touch higher.

then used the checker and got 5.5 ppm.

they essentially helped validate each other

in any event, more than close enough for rock and roll, and, again, my thanks.