After testing the Salifert NO3, PO4, and K kits earlier this year, my confidence in using these kits grew. They're great for general assessment of EI-dosed tanks; for example, "is my NO3 at or around 20ppm? Then I'm good!"
However, I've been experimenting with a nonlimiting (EI) dosing structure that involves 1) front loading after weekly WC, then 2) dosing at/near the daily levels of consumption.
In order to do this, I need to KNOW what my daily consumption levels are, which requires more specific ppm readings than what most kits can provide. Looking at the API/Salifert NO3 test kits, you cannot possibly know if you truly have 15ppm or 20ppm because of the variation in readings, light levels, etc.
Reefers are way ahead of us with saltwater colorimeters, like this one from Hanna:
The colorimeter comes calibrated from the factory to read the difference between the reading without reagents vs the reading with, and can determine how much NO3 is in the water based on how the cuvette with reagents differed from the one without.
Hanna’s internal calibration curve assumes:
There are a few threads on The Planted Tank that tried to remedy this, but none were using the actual methods that we do in a laboratory setting to create the "curve" for colorimeter results.
So, let's fix it!
Next, we need to make a few stock solutions from RO/DI water and KNO3, then dilute the concentration into a few known stock solutions.
The stock solutions I created were:
I ran both colorimeters at the same time, from the same stock solutions. Here were the results:
I marked the checkers #1 and #2, kept the cuvettes spotless with rubbing alcohol and microfiber cloths, and never mixed cuvettes, solutions, etc (proper lab protocol for colorimetry).
This took about 4 hours to run and $30 in reagents with two $75 kits. If you want to donate, let me know lol
The differences are due to reaction timing, temperature, mixing, and small optical differences. This is normal for cadmium reduction methods (like the Salifert kits).
There is a ±3ppm reading accuracy below 20ppm, a ±2ppm reading between 20ppm and 50ppm, and a ±4ppm accuracy above 50ppm. This is pretty neat compared to trying to determine what shade of whatever your card is displaying with regular test kits. From what I could find online, this is exactly what we expect from a seawater-calibrated curve applied to freshwater in colorimetry. While it's not pinpoint precise, it's still really useful and another option for testing Nitrate levels in our tanks.
Some other observations:
Time is of the essence. Like many cadmium-based kits (like salifert) you really should be setting timers to get accurate results. However, unlike the salifert kits which change color drastically over the course of even 1-2 minutes, this test kit moves much slower and has a much longer window.
Here's how I use this kit:
Here's what it looks like:
Combining the Hanna High Range Nitrate Colorimeter with this conversion calculator has been extremely accurate (tested against Salifert test kits to the best of my abilities) as well as for exactly what I'd expect while using my other calculator, Rocco's Nutrient Accumulation Calculator, when testing my tank's water for the last few weeks.
However, I've been experimenting with a nonlimiting (EI) dosing structure that involves 1) front loading after weekly WC, then 2) dosing at/near the daily levels of consumption.
In order to do this, I need to KNOW what my daily consumption levels are, which requires more specific ppm readings than what most kits can provide. Looking at the API/Salifert NO3 test kits, you cannot possibly know if you truly have 15ppm or 20ppm because of the variation in readings, light levels, etc.
Reefers are way ahead of us with saltwater colorimeters, like this one from Hanna:
How it works:
To dumb it down as much as possible, colorimeters have an internal light one one side, and a sensor on the other. You insert a vial (called a "cuvette") of tank water, and the colorimeter flashes the light through the cuvette into the sensor to calibrate for "zero". Then, you remove the cuvette, add your reagent/testing powder, shake, let it sit, insert it back into the colorimeter, and it flashes the light into the sensor again.The colorimeter comes calibrated from the factory to read the difference between the reading without reagents vs the reading with, and can determine how much NO3 is in the water based on how the cuvette with reagents differed from the one without.
The problem with using it for fresh water:
These colorimeters are calibrated specifically for salt water use from the factory.Hanna’s internal calibration curve assumes:
- Seawater background absorbance
- Seawater refractive index
- Seawater reaction completion timing
- Blank absorbance is lower
- The same color intensity maps to a higher ppm value on the seawater curve
- The colorimeter does completely work for freshwater just like any colorimeter would, the values are just not mapped to
There are a few threads on The Planted Tank that tried to remedy this, but none were using the actual methods that we do in a laboratory setting to create the "curve" for colorimeter results.
So, let's fix it!
Gathering real data:
First, I bought not one, but TWO Hanna High-Range NO3 kits to test, as well as tons of extra test reagent packets.Next, we need to make a few stock solutions from RO/DI water and KNO3, then dilute the concentration into a few known stock solutions.
The stock solutions I created were:
- 5ppm NO3
- 10ppm NO3
- 20ppm NO3
- 30ppm NO3
- 50ppm NO3
- 70ppm NO3
I ran both colorimeters at the same time, from the same stock solutions. Here were the results:
I marked the checkers #1 and #2, kept the cuvettes spotless with rubbing alcohol and microfiber cloths, and never mixed cuvettes, solutions, etc (proper lab protocol for colorimetry).
- 5ppm results round 1: 8.1, 8.2
- 10ppm results round 1: 12.9, 13.0
- 20ppm results round 1: 23.0, 22.3
- 30ppm results round 1: 34.7, 32.6
- 50ppm results round 1: 53.3, 57.8
- 70ppm results round 1: 68.6, 74.0
- 5ppm results round 2: 7.9, 9.1
- 10ppm results round 2: 13.9, 13.8
- 20ppm results round 2: 25.0, 23.1
- 30ppm results round 2: 36.3, 34.9
- 50ppm results round 2: 52.4, 57.0
- 70ppm results round 2: 67.0, 67.4
This took about 4 hours to run and $30 in reagents with two $75 kits. If you want to donate, let me know lol
Findings and Results
The kit is not bad! At each concentration, readings cluster tightly.The differences are due to reaction timing, temperature, mixing, and small optical differences. This is normal for cadmium reduction methods (like the Salifert kits).
| True (Y) | Avg Meter (X) |
|---|---|
| 5 | ~8.3 |
| 10 | ~13.4 |
| 20 | ~23.4 |
| 30 | ~34.6 |
| 50 | ~55.1 |
| 70 | ~71.0 |
There is a ±3ppm reading accuracy below 20ppm, a ±2ppm reading between 20ppm and 50ppm, and a ±4ppm accuracy above 50ppm. This is pretty neat compared to trying to determine what shade of whatever your card is displaying with regular test kits. From what I could find online, this is exactly what we expect from a seawater-calibrated curve applied to freshwater in colorimetry. While it's not pinpoint precise, it's still really useful and another option for testing Nitrate levels in our tanks.
Some other observations:
Time is of the essence. Like many cadmium-based kits (like salifert) you really should be setting timers to get accurate results. However, unlike the salifert kits which change color drastically over the course of even 1-2 minutes, this test kit moves much slower and has a much longer window.
Here's how I use this kit:
- Use a 10mL syringe with stainless steel needle to sample tank water into clean cuvette
- Insert into colorimeter, take C1 "calibration" blank reading
- Remove the cuvette by the cap. Cut reagent packet, pour into cuvette, immediately start a 2 minute timer, and begin shaking.
I use a Intllab Vortex Mixer to mix for the 2 min duration, but you can just shake hard. Do not get fingerprints on the middle of the cuvette. - Insert into colorimeter and press and hold the button to start the 7-minute timer. After 7 minutes, you'll have your reading. Then...
We can also use this data to fit a new calibration curve, and make a new calculator that anyone can use to take readings from their freshwater aquarium with this kit:
Here's what it looks like:
Combining the Hanna High Range Nitrate Colorimeter with this conversion calculator has been extremely accurate (tested against Salifert test kits to the best of my abilities) as well as for exactly what I'd expect while using my other calculator, Rocco's Nutrient Accumulation Calculator, when testing my tank's water for the last few weeks.
