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Test-Kit Primer/ Testing the kits

I've started a Primer on Test Kits for the Planted tank at 
http://www.brainyday.com/jared/aquarium/testkits.htm which, by coincidence, 
links to Chuck's Nitrate Doser.

I just tested my LaMotte Nitrate kit (mod. 3110) using Chuck's measurements 
for a 14 ppm solution (1 tsp potassium nitrate in 500 mL distilled water; 
one mL of that in 500 mL water). I tried it out with two different kitchen 
measuring spoons (not all are super accurate).

Spoon #1. Reading was 4.5 ppm nitrate-nitrogen (interpolating between the 
references for 4.0 and 6.0), which is 20 ppm nitrate.

Spoon #2. Reading was  6.0 ppm nitrate-nitrogen, which is 26 ppm nitrate.

(BTW, the eight reference solutions in the comparator, converting to from 
nitrate-nitrogen to nitrate and rounding, are  (0), 1, 2, 4, 9, 18, 26, and 
44 ppm.)

So I think we are OK here, considering all the variables -- my spoons, 
leveling the spoonful, my test procedure (measuring the reagents, 
interpolating). I took the 1 mL with a 1 mL graduated dropped, which of 
course may not have been accurate. One should repeat the test several times 
with the same spoon as well.

I personally think that LaMotte's sealed reference liquids in the 
comparator are accurate -- the question arises whether the test as 
performed gives you a test color that reflects the true concentration of 
nitrate. The fair way to test (judge) a test kit would be in the lab.I may 
well be testing my measures. As I mention on my Primer page, often its 
enough to have a "good idea" of the actual level and be more concerned with 
whether the tank is going up or down from week to week.


Jared Weinberger