On Sun, 15 Feb 2004 01:39:28 GMT, The Kenosha Kid
wrote:

I switched to a Hagen Nutrafin test kit with several different tests
in the same kit. It has a test for NO3 which I used to cover using a
Tetra test kit.

I ran tests for NO3 using both kits on samples from the same body of
water. The new (Nutrafin) kit gave me a reading at or below 5 mg/l
while the Tetra kit gave me a reading at or excess of 50 mg/l.

I repeated the tests twice and got the same results.

Apart from the Tetra kit being a year old are there any other reasons
for these results to be so far apart?

Update


Last week I made a trip to Dolphin Pet Village with a vial of my water
and had them test it.

Dolphin, using yet another set of reagents, came in at 10 mg/l or
below so it looks like the old Tetra kit is fubar and the Nutrafin kit
with it's reading of 5 mg/l is ok. It suggests that there is a
plus/minus 5 mg/l tolerance on the test.