Accurate NO3 Test with Hanna ULR P Checker

purp · Mar 30, 2020

I'm working on generating a curve for the salifert kit right now. Baking some KNo3 overnight and need to make up some reference seawater matrix. Feels good to flex the old chemistry brain.

purp · Mar 31, 2020

So in this same vein, can someone talk me through the benefit of using a saltwater analogue for reference solution (just iodized salt) vs using a fresh aquarium salt mix that is then spiked?

Rick Mathew · Mar 31, 2020

purp said:
So in this same vein, can someone talk me through the benefit of using a saltwater analogue for reference solution (just iodized salt) vs using a fresh aquarium salt mix that is then spiked?

My experience is that commercial salt mixes can have elevated levels of nitrates so that would interfere with your calibraton curve...I use Reagent grade sodium chloride...from Amazon...

purp · Mar 31, 2020

what level nitrates have you seen in the past?

Is there an appreciable difference between reagent and morton's?

taricha · Mar 31, 2020

Salt mixes can have a few tenths of a ppm of ammonia, which can then lead to nitrate readings (nitrite interference also an issue) in the 0.5 to 1.0ppm ballpark.

Rick Mathew · Mar 31, 2020

purp said:
what level nitrates have you seen in the past?

Is there an appreciable difference between reagent and Morton's?

I don't know the answer about the reagent grade and morton's....Reagent grade is 99.99% sodium chloride so I feel confident it is low in contamination....I don't know about the analysis of Morton's

Here is a chart of some analysis of commercial salt and the NO3 levels

Also I have attached a PDF of analysis of commercial salts

For me I have measured up to as high as 1-2 ppm...most of the time in the .5-.7 ppm....

hope this helps

rick

TABLE III Nutrients (micromoles per kilogram)
	PO4	NO3:N	NH4:N	SiO3:Si (*color)	SiO3:Si (**ICP)	DOP	DON:N	TOC:C

Seawater	0.20	0.20	0.20	5.0	5.0	0.20	10.0	50.0
Instant Ocean	0.05	1.00	10.2	4.2	16.0	0.10	2.9	29.0

Tropic Marin	1.20	2.20	0.55	3.2	14.0	0	5.5	32.0
HW Marine Mix	0.46	1.63	9.2	11.5	29.0	0.2	8.2	29.0

Reef Crystals	0.32	5.0	7.8	5.9	46.0	0.2	6.3	28.0
Red Sea Salt	0.37	0.79	5.2	4.5	17.0	0.1	1.9	29.0

Kent	0.16	2.05	11.9	4.1	37.0	0.1	2.4	28.0
Coralife	0.95	6.30	8.4	2.7	18.0	0.2	11.2	28.0

SeaChem	0.57	18.4	0.7	11.3	23.0	0.1	3.1	22.0
Molar mass	30.9738	14.0067	14.0067	28.086	28.086	30.9738	14.0067	12.011

purp · Apr 1, 2020

For the salifert kit, anything over 5 ppm was over 200 on the meter, even at a 10:1 post rxn RODI dilution.

I ran the reaction sample in the cuvette and zerod the meter with 0 ppm salinity matched sample. At low levels, (less than 1) it was very repeatable. However, i didn't have many standards made up at low levels (<1 ppm). I used up all my reagent before I could rerun more discrete low-level standards.

Massive grain of salt, but here's my equation.

y = 42.678x + 7.0975

R2 of 97% on four standards (0, .781. 1.56 and 3.125). Don't laugh, it was a serial dilution down from 25

. These were not all run in triplicate, so again, until this can be confirmed don't use this as gospel.

purp · Apr 2, 2020

And just to be clear, the Salifert kit uses 1 mL sample volume. I completed the rxn in the cuvette with 1 mL sample, and then diluted with RODI to the 10 mL line.

taricha · Apr 2, 2020

Nice!
post data table or graph?
and the x and y in your equations are...
[hi736 reading] = 42.68 [ppm NO3] + 7.10
that correct?

(I didn't realize the salifert kit only takes a 1mL sample. There are situations where having a small sample volume would really help out.)

purp · Apr 2, 2020

correct.

taricha · Apr 2, 2020

purp said:
correct.

That's impressive color formation for a 1/10 dilution! That and a 1mL test volume means I can totally come up with good uses for it.
hey @Rick Mathew used Salifert NO3 any?

purp · Apr 2, 2020

i didnt have enough reagent to do a side by side with the salifert container, but when I did the salifert test in the cuvettes, the color seemed *very* bright compared to the color cards with known concentrations. These were lab prepared standards, so im pretty confident they were well made. The only x-factor would be the salinity adjustment I did.

The other variable is I didnt really control the development time well. At the higher end of the spectrum, it continued to develop longer than I would have suspected. At the low end, 3 minutes was plenty and measured consistently on the hanna.

Honestly I'll probably buy a red sea next since the method is well constrained, but I wouldnt mind trying again if I could get another cheap/free salifert kit.

Rick Mathew · Apr 3, 2020

taricha said:
That's impressive color formation for a 1/10 dilution! That and a 1mL test volume means I can totally come up with good uses for it.
hey @Rick Mathew used Salifert NO3 any?

I have not done any work with the Salfert kit...but it is interesting the level of color this kit produces...might be worth a look to see if could potentially offer a wider range of testing and possible give more accurate readings in the low range.

purp · Apr 4, 2020

Man, i just picked up the red sea no3/no2 and ran some standard tests on it. They were all within 0.5 ppm. I'm very impressed with the results of this method! I dosed my display and my frag with kno3, tested before and after. It a) supported my tank water volumes and b) gave me accurate results. I'm very pleased!

Rick Mathew · Apr 4, 2020

purp said:
Man, i just picked up the red sea no3/no2 and ran some standard tests on it. They were all within 0.5 ppm. I'm very impressed with the results of this method! I dosed my display and my frag with kno3, tested before and after. It a) supported my tank water volumes and b) gave me accurate results. I'm very pleased!

Great to hear...Thanks for the feedback!

Superlightman · Aug 22, 2020

i heard they is finally a nitrate test available?

Rick Mathew · Aug 22, 2020

HI781 Saltwater Nitrate Low Range Checker - Hanna Instruments

Shop The Best Saltwater Aquarium Equipment & Supplies at Saltwater Aquarium. We Carry Everything you will Need for your Fish Tank.

www.saltwateraquarium.com

Not yet released...Sept 30..I have one preordered to give it ima test run

purp · Oct 22, 2020

lol they finally did it. its involved, they ended up using a filtrate disc as well.

What I find interesting is that they make no mention of salinity matching in their dilution, and then also that the undiluted analytical range is very low (0-5).