# Wrong Nitrate Reading of reference solution



## Gorillastomp (24 Mar 2022)

Hey guys,

I recently bought an Hanna Nitrate Colorimeter Tester and it gives me a double dose result.

I did a reference solution of KNO3 using Rotalabutterfly fertilizer dosing page.


This is the result :






So i dosed 10ml of that solution in a 2L container. When i do the test it should gave me around 10ppm but it reads 20ppm. I am wondering is the math on rotalabutterfly off or my KNO3 isn't really kno3 or i have a defective unit ?

I did this reference test because last week when i did front load my aquarium it gave me a double dose result as well.

i test that out with spoon measurement and via scale (incase i had a defective scale) both gave pretty much the same result.


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## Hanuman (24 Mar 2022)

Gorillastomp said:


> I am wondering is the math on rotalabutterfly off


It's not off. 









As you can see all numbes match RotalaButterfly's calculator. What could be off is the 10ml you are adding. Could you be dosing 20ml mistakenly?


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## Gorillastomp (24 Mar 2022)

i am using a graduated vial to mesure the 10 ml

when i dosed my tank i dry dosed it, so i guess my tester shows double, i will reach out Hanna instrument i guess.

thanks!


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## Ria95 (24 Mar 2022)

Very likely the meter functions well and  your measurement is close to the target.  First of all glad you noticed the issue. Many others did not , including that angry youtube doctor who tested everything but can't show his own data somehow . He thinks this meter works spot on out of the box for his goldfish tanks.

The issue... the first word in the test kit name : 'Marine' . The calibration curve and test kit reagent mix (likely) are done for another water matrix. It's  one of the issue why the general advice is not to be overly reliant on test numbers. Even if a kit performs wonderfully in  pure water + test substance, this performance may not be so spot on in actual aquarium water because the matrix is more complicated. In this case , the kit will perform better in 'pure' marine water +test substance ... that's the intended market.

Back to the Hanna Checker, the person I'm  in contact with also found the factor between actual and reported values to be around 0.5 (variation depending on the matrix of the tank) when testing freshwater tanks. To get aproximate values you can use this factor or get better results by adjusting the sample to  35ppt with marine salt as he does.

Hope this helps with the issue you have been experiencing.


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## Wookii (24 Mar 2022)

Ria95 said:


> Very likely the meter functions well and  your measurement is close to the target.  First of all glad you noticed the issue. Many others did not , including that angry youtube doctor who tested everything but can't show his own data somehow . He thinks this meter works spot on out of the box for his goldfish tanks.
> 
> The issue... the first word in the test kit name : 'Marine' . The calibration curve and test kit reagent mix (likely) are done for another water matrix. It's  one of the issue why the general advice is not to be overly reliant on test numbers. Even if a kit performs wonderfully in  pure water + test substance, this performance may not be so spot on in actual aquarium water because the matrix is more complicated. In this case , the kit will perform better in 'pure' marine water +test substance ... that's the intended market.
> 
> ...



Was going to post the same thing. I looked into getting one of these, but from  the product description:



> . . . accurately determine high levels of nitrate for *saltwater aquariums and marine applications* . . .



and the specification:



> This checker has been developed to work with seawater samples.


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## dw1305 (24 Mar 2022)

Hi all,


Ria95 said:


> The issue... the first word in the test kit name : 'Marine' . The calibration curve and test kit reagent mix (likely) are done for another water matrix. It's one of the issue why the general advice is not to be overly reliant on test numbers. Even if a kit performs wonderfully in pure water + test substance, this performance may not be so spot on in actual aquarium water because the matrix is more complicated. In this case , the kit will perform better in 'pure' marine water +test substance ... that's the intended market.


Exactly that, what @Ria95 and @Wookii have said.

It is actually easier to test sea water because it has a <"known chloride ion (Cl-) content"> and Cl- is an ion that interferes with the measurement of NO3-.  There are <"alternative techniques"> for estimating nitrate levels and I'd argue that they are <"actually more effective"> because the <"leaf colour and growth"> of a floating plant is a pretty good proxy <"for fixed nitrogen levels in the water">.

cheers Darrel


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## Gorillastomp (24 Mar 2022)

I did sent a message to hanna and waiting for a response. And yes this where i have a bit overlooked, the marine part.

While the phosphate tester and the iron tester seems to be near the "real" value.


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## dw1305 (24 Mar 2022)

Hi all,


Gorillastomp said:


> While the phosphate tester and the iron tester seems to be near the "real" value.


A lot of this <"comes down to solubility">. The problem with iron (Fe ++(+)) and phosphorous / phosphate (P / PO4---) is usually keeping them in solution, but in terms of testing for them them is advantageous because you have a <"choice of insoluble coloured compounds"> that you can use for colormetric ("intensity of colour") testing.

The problem with monovalent ions like nitrate (NO3-) (and K+ etc.) is the one above in reverse,  all their compounds are soluble which means that they are always plant available, but it is much more difficult <"to find insoluble coloured compounds"> that we can measure colormetrically.

cheers Darrel


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## Zeus. (24 Mar 2022)

I just trust the 'maths' , tests and meters are subject to errors and the maths is also free to use.


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## Gorillastomp (24 Mar 2022)

dw1305 said:


> There are <"alternative techniques"> for estimating nitrate levels and I'd argue that they are <"actually more effective"> because the <"leaf colour and growth"> of a floating plant is a pretty good proxy <"for fixed nitrogen levels in the water">.


Interesting reading, i don't know how i pass over this since you seem to refer to that pretty often.



> Because plants needs about x10 the amount of nitrogen (N) and potassium (K) compared to phosphorus (P), (and x3 times more phosphorus than any of the other elements) deficiencies are most likely to be nitrogen or potassium. Other options that cause chlorosis are magnesium (in older leaves) and iron (in younger leaves). *Nitrogen and potassium deficiencies show up in old foliage first, and both cause yellowing (chlorosis) and smaller leaves.*



How you know if it's Potassium deficiency vs Nitrogen  ?

Recently i had yellowing issue in my new growth of staurogyne repens, i thought it was an iron deficiency  but it seems it was a Potassium case. Increasing my iron did nothing while increasing my potassium made the leaf greener.


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## Gorillastomp (25 Mar 2022)

Ria95 said:


> First of all glad you noticed the issue. Many others did not , including that angry youtube doctor who tested everything but can't show his own data somehow


😂 i get the reference.



Ria95 said:


> Back to the Hanna Checker, the person I'm in contact with also found the factor between actual and reported values to be around 0.5 (variation depending on the matrix of the tank) when testing freshwater tanks. To get aproximate values you can use this factor or get better results by adjusting the sample to 35ppt with marine salt as he does.



I am not familiar with reef tank, how would i raise my sample to 35ppt of salinity ? Do you have any mixing ratio i can use to reach said salinity level ?


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## Hanuman (25 Mar 2022)

dw1305 said:


> I'd argue that they are <"actually more effective"> because the <"leaf colour and growth"> of a floating plant is a pretty good proxy <"for fixed nitrogen levels in the water">.


A color blind person would disagree with you. He still got the math though.


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## dw1305 (25 Mar 2022)

Hi all,


Hanuman said:


> A color blind person would disagree with you.


Yes, this actually comes up in one of @jameson_uk's threads, where he is trying to use the "Duckweed Index", but is hampered by <"red-green colour blindness">. My dad was red green  colour blind and it made <"Raspberry picking interesting">.


Gorillastomp said:


> How you know if it's Potassium deficiency vs Nitrogen ?


I don't. I don't actually <"try and diagnose"> any of the deficiencies of <"mobile elements">.

If the older leaves are yellow I just add a complete fertiliser mix. <"Liebig's limiting nutrient"> likely to be nitrogen (N) or potassium (K), purely because they are the elements that plants need most of, but magnesium (Mg) etc are also a possibility.


Gorillastomp said:


> Recently i had yellowing issue in my new growth of staurogyne repens, i thought it was an iron deficiency but it seems it was a Potassium case. Increasing my iron did nothing while increasing my potassium made the leaf greener


They should cause yellowing in different parts of the plant, <"potassium in older leaves"> and <"iron (Fe) in new leaves">.

cheers Darrel


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## JacksonL (25 Mar 2022)

I was wondering the other day if these would work ok in freshwater. Guess not.
I have one of the low range phosphate ones left over from my reef tank days and that works well in freshwater, but it doesn’t have the “Marine” stamp on it


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## Gorillastomp (4 Apr 2022)

Just a heads up about this,  I bought marine salt today and set the sample to around 35ppt as suggested by @Ria95.  

The value i am getting is 8.3 ppm Nitrate with a solution of 10 ppm. 
This is far more precise than without the salty sample.

Keep in mind this is not some laboratory 10ppm solution, my scale can be off a little etc. 

To me it's precise enough to use it like that.


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## Simon Cole (4 Apr 2022)

@JacksonL  The Hach Lange DR300 is a decent-enough colorimeter if you have freshwater samples and don't want to use a UKAS accredited laboratory.


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## Ria95 (14 Apr 2022)

Glad it also worked for you. I would say the value you got is within the specifications of the meter even with the modification


*Accuracy @ 25°C/77°F*±2.0 ppm ±5% of reading @ 25 °C

and in my opinion plenty suitable for our 'informative' testing purposes. They seem to produce more and more of these handheld meters so a freshwater one may  be available at some point.  Rhetorical question ... where is the accuracy figure on test strips and liquids kits 1 month after opening them?


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## Gorillastomp (14 Apr 2022)

Liquid test seems to be accurate for a long time. After a year i was still getting the same result. 

I use test strip at my job to detect if there is free chlorine in water, after around 2 month the bottle is open i get wacky results.


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