KNO3 dosing and low range NO3 testing

[otimer]

Hello members,
My tank NO3 level is between 0.25 and 2.0 ppm by Rad Sea NO3 pro test kit.
In order to manage NO3 levels in a narrow range, I am planning to dose KNO3 solution.
I prepared a dosing solution as follows.

I made 1,000ppm NO3 base solution adding 1,630mg of EP grade 99% KNO3 reagent powder in 1,000ml of 35ppt salt mix (0ppm NO3 by Red Sea NO3 pro test kit).
This is one of well-known ways to prepare a NO3 dosing solution. and also it can be made by accurate calculations by mole weights.

Kno3 (Potassium Nitrate) Dosing Instructions!

Fellow chemistry inclined reefers, I'm currently experimenting with Aquavitro Synthesis to raise my nitrates but I believe I'm going to switch to Potassium Nitrate. Upon some research I found this equation (see pictures) to be the general rule of thumb. My problem is I have a 160g system and I...

www.reef2reef.com

This base solution was diluted with RODI water or new salt mix to make 1, 4ppm and 17.7ppm NO3 solutions.

The test results with the Red Sea NO3 pro test kit were about 0.5 ppm for the 1ppm solution and less than 2ppm for the 4ppm solution.
The solutions were stored overnight, but the test results were same. I prepared the base solution several times using rodi water or new salt mix using different measuring devices (electronic percision scale, mass cylinders and syringes), but the results were same.
I have done with brand new Red Sea NO3 pro test kit having expriry date 0f 02/2022, but the results were much lower than those from old test kit.

I do not have any doubt on the accuracy of the test kit, because I performed cross testings for the test samples (2 and 10~15ppm NO3) from local reefers tank water with Red Sea test kit (rodi 4:1 diluted for 10ppm sample), Salifert NO3 test kit and Lamotte 3110-01 test kit. The results with all three were almost same.
Also I prepared KNO3 solutions of 4.42ppm and 17.70ppm NO3 for 1ppm and 4ppm N-NO3 using the above base solution, and tested with Lamotte 3110-01 N-NO3 test kit.
The results were exactly 1 and 4 ppm N-NO3. So I consider my base solution and dilution processes are not bed.

Also I tried to test the Brightwell aquatics NeoNito (as far as I understand, it is KNO3 solution.), the results were much lower than the calculated from the concentation on the instructions.

1. THe result of the old R.S NO3 pro test kit for the diluted 2ppm KNO3 solution : seems 1.5ppm

2. The result of the new R.S NO3 pro test kit for 2ppm KNO3 solution : seems 0.5ppm

3. 17.70ppm NO3 solution for 4ppm N-NO3 and test result with Lamotte 3110-01 N-NO3 test kit : 4ppm N-NO3
The blue cap on the uppe-rmid of the image is the test vial.

I reported and asked Red Sea Customer Service about this two months ago, I got a reply that their scientist is reviewing about my ticket.
No reply yet upon my couple of remindings.

4. Quesations
1. Does anybody have this kind of experience?
2. Can I dose KNO3 in my tank monitoring with Red Sea NO3 pro test kit?
3. Is there any other recommendable alternative NO3 test which can measure 0~1.0ppm?

Thanks in aqdvance for your input.
Son in Seoul Korea

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5. My Tank is ;
1.Size : 1500*700*600h Peninsular
2.Net Water Volume : 600L
3.Return Pump : Vectra M1 *2 turn-over 7, Bean Animal Overflow System
4.Wavemaker : Vortech MP40qd *4
5.Lighting : GHL Mitras LX7206 *4 + Orphek LED Bar OR2 1200 *2
(15500K 5hr 17500K~21000K Ramp up/dn 4hr, top 350par ~ bottom 200par)
6.Major E Dosing : Calcium Reactor Geo's 612 50% Balling w/ dosing pump 50%
7.Trace Elements Dosing : w/ Balling Dosing Pump
8.Protein Skimmer : R.E Bubble King D.C 200 w/ RD3
9.NO3 Export : Denitrator w/ Seachem Denitrate 8L
10.Water Change & ATO : 1.5%/d automatic (10%/week), by Profilux 4
11.NO3 & PO4 Export : Macro Algae Reactor Pacific Sun MAR ProM
12.Parameters
- Temp : 26.3'C w/ DBC-200 GHL Cooling Fan
- Sal : 34.0ppm (GMH3450 w/ Ricca 50mS Cal Solution)
- Ca : 420ppm (Salifert)
- Mg : 1350ppm (Salifert)
- Alk : 130ppm (Hanna Alk ppm)
- K : 400pm (Salifert)
- NO3 : 0.75ppm (Red Sea NO3 pro)
- PO4 : 0.02+/-ppm (Hanna Checker P ULR)
13. Accessories : GHL Profilux 4 Aquarium Controller, Ozone Generator Poseidon 200,
GHL KH Director, 4" Filter Sock * 3,, GHL Doser 2.1 4P *2, DIY Power Failure Backup 12 hr,

 

[Sallstrom]

@Lasse

 

[Lasse]

The two sample photos in the read Sea (1 and 2) - what did you use as dilution - 35 psu saltwater or RO water? These NO3 tests are very sensitive to disturbing ions and if you should do a an accuracy test - the spike method is the one I would do. It means that you analyse your saltwater and take out a litre of it. after the first analyse you spike the 1 L sample with a known amount of NO3 and analyse again. The differences between this two analyses should be near the known spike.

Chloride is known to lower the readings of nitrate in most tests. The manufacturer needs therefore to incorporate this in the colour scale - it means that you can´t use a saltwater test on fresh water or RO water and the other way around for fresh water tests

In low measurements of Nitrate - nitrite will disturb the readings. I have leaved Red Seas test and instead I use Tropic Marine Pro test that also give you a opportunity to measure nitrite and do a compensation for NO2 concentration. Observe - they have both a normal and Pro methode and the Pro is - IMO - best. Give you better NO2 readings. Please see here for discussion of nitrite´s importance in nitrate measurements

Sincerely Lasse

 

[otimer]

The two sample photos in the read Sea (1 and 2) - what did you use as dilution - 35 psu saltwater or RO water? These NO3 tests are very sensitive to disturbing ions and if you should do a an accuracy test - the spike method is the one I would do. It means that you analyse your saltwater and take out a litre of it. after the first analyse you spike the 1 L sample with a known amount of NO3 and analyse again. The differences between this two analyses should be near the known spike.
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Hello Lasse, thanks for the detail information. I appreciate your valuable comments.
I diluted the test samples with 35ppt 0ppm NO3 salt mix, and I did with rodi water as well. The results were exactly same. As far as I understand, Red Sea NO3 pro test kit is not influnceed by salinity of samples, as their instructions say that we may dilute samples with rodi water for high range testing. I believe that there was no mistake in the testing procedure as my background is instrument engineer have handled lots of titration test equipment, and I strictly followed with their instructions.

I will get a Tropic Marin test kit and try the tests again shortly. I will be back with the results.
Sorry for late response due to the time difference.
Thanks again.

Son

 

[Lasse]

This base solution was diluted with RODI water or new salt mix to make 1, 4ppm and 17.7ppm NO3 solutions.

The test results with the Red Sea NO3 pro test kit were about 0.5 ppm for the 1ppm solution and less than 2ppm for the 4ppm solution

I have problem to understand this. Red Sea NO3 pro give the answer in NO3 and your 1 ppm and 4 ppm solutions is in NO3-N as I understand. I understand the math further down; 1 ppm NO3-N -> 4.42 ppm NO3 and 4 ppm NO3-N -> 17.7 ppm NO3 - but I do not understand the quote above

Sincerely Lasse