500 Tests Possible for Red Sea NO3 Test

[Dan_P]

Just recently I discovered that the Red Sea test for nitrates uses a whopping 16 mL sample. I got to wondering whether it could be scaled down to 1 mL. This would mean reagents for 100 tests becomes enough for 1600 tests for ~$30. When I purchased the kit, I found out that two of the three reagents are solids, so, I decided to try only a 1/5 scale down (500 tests per kit) on a 1.8 ppm NO3 standard I prepared form 99% NaNO3.

The scale down worked AND the color is nearly the same hue and intensity as the Salifert nitrate test result, which means the Salifert color chart can be used with the Red Sea test to interpret the results. A downside is that you can't use the nice comparator that comes with the Red Sea kit.

I used digital image colorimetry to measure the absorbance in the green channel of the test solutions:

Salifert: 0.079
Red Sea: 0.071

These were indistinguishable differences to the eye. For both tests, the test color looked darker than 1 ppm and lighter or the same as 2.5 ppm on the Salifert color chart when using the low range method.

I measured the solid reagents with 1 mL syringes with the ends cut off and the plungers pushed in to give a 0.03 mL volume to contain the reagents.

[GimpyFin]

That's cool. Just out of curiosity, though, how often do you test Nitrate? The kits generally expire within a year, maybe a little longer. (I'm lucky to go through 1/4 of the reagents on the Red Sea Pro before I get a new kit.)

[Dan_P]

That's cool. Just out of curiosity, though, how often do you test Nitrate? The kits generally expire within a year, maybe a little longer. (I'm lucky to go through 1/4 of the reagents on the Red Sea Pro before I get a new kit.)

For me, it is small sample size that is the most important part of this discovery, though, running triplicates tests and trending nitrate levels are now inexpensive. I agree, for the average person, this might be a yawn.