[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Nitrate test kits
Eric wrote,
Regarding the comments about the discrepancy between the measurements:
About a year ago I spoke with a Hach field rep and he said that the
particular kit I had was subject to error induced by the characteristics
ofthe tester. That is to say, the test results were variable to a
significantdegree by interpretation of the instructions by the tester.
Theinstructions say add the reagent, cap the test tube, and shake
vigorouslyfor exactly one minute. Well, how vigorous is vigorous and from
what pointin the process do you start the "exactly one minute" count as it
takes afew seconds to empty the reagent packet into the test tube and cap
the tubebefore you can shake it. I never got a verification from him about
theeffects of my interpretation and testing procedure because I didn't
havethe test kit with me when I saw him and I wasn't about to pay for a
house
call. I have not read the article in the magazine_PracticalFishkeeping_
that Roy alludes to but this may be the reason for the discrepancy
mentioned; I'll read it if I can find it. Roy, can you elaborate on the
article?
This was exactly the gist of what they were saying. Different testers
interpreted the results to give different readings. It appears it was not so
much the way that they carried out the tests, but the comparison of the
result with the colour charts. Results were better if the actual
concentration was close to one of values shown on the colour chart but if it
fell in-between then there was much more variation. Nontheless, in many
cases all, or the majority, of the testers interpreted the results to mean
much higher or lower levels than it actually was. This was not just a matter
of being a feww ppm off but several fold off. In our situation people using
these kits could well be adding nitrate to tanks that already exceeded the
recommended range, or, conversely, not adding nitrate in the belief that
there is sufficient present in their water.
How you interpret this is up to you. As an individual testing in a
consistent way you can probably at least detect trends in the nitrate
levels. However, if you want to be sure of the actual levels you will need
kore acurate tests than the average Hobbyist kit. On the other hand it may
be an argument for relying on observation more than testing.
Regards, Roy.
_________________________________________________________________
Chat online in real time with MSN Messenger http://messenger.msn.co.uk