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Checking the NO3 test kit with a reference

I see a lot of folks having trouble with NO3 test kits and seeing if they
are giving the right readings etc. For those folks that want to check those
funny readings on their NO3 test kits here's a simple way to do this:

A level 1/4 tsp = 1.67 grams on average(Cooke's/Grant's brands => based on
20 samples and 3 different runs with 3 different teaspoons on an analytical
microscale). You can add this to a 1 liter pure H2O. This will give you
.61325 grams of NO3 in that water (and .387 grams of K+). Since ppm =
mg/liter you'll now have 613.25ppm (or no# of milligrams in one liter) NO3
in this sample. Take 10mls of this solution and add it to another 1 liter of
pure H20. 10mls/1000ml in a liter = 6.1325ppm of NO3 in this reference
sample. Gauge your test kit against this. The ref solution is pretty
accurate(+,- 0.2ppm) even if you are a little off(weights/volume, different
1/4 teaspoons, ml doses are a little off, KNO3 not 100% pure etc). Try to be
accurate though. This should get a better idea of what's happening with all
the kits that are out there and their accuracy within the range plant folks
need for NO3 measurements.

+ or - 1ppm is not going to make or break folk's tanks. If you are this
close and are trying to maintain 5-10ppm NO3, you are not going to have any
issue with that. 

Tom Barr