Xref: 127.0.0.1 rec.aquaria.freshwater.plants:73123

On Wed, 18 Jun 2003 23:37:26 -0600, Chuck Gadd wrote:

Some nitrate test kits report the results of nitrate-nitrogen.
For those kits, they report only the nitrogen portion of the nitrate.
To get to ppm Nitrate, you need to multiply the value by 4.4, which
would give you 13.2, pretty close to what you should get for the
reference solution.

According to the literature in the Hagen Nitrate Test Kit:

--------------------------------------------------------------------------------
Nitrate Test
For nitrate as nitrogen (NO3-N), divide result by 4.4
--------------------------------------------------------------------------------

This implies that the kit is 'supposed' to read Nitrate directly.
And with this in mind, the kit is not accurate.

Also, to insure that the information I am tendering is accurate, I
remixed the standard solution and re-tested with each kit.

The Hagen kit contains a reagent #3 that is apparently comprised of
zinc dust mixed with N-1 Naphthylethylene-diamine Di HCl. Each time
the test is run, a different result is obtained. Apparently, the zinc
does not stay in suspension correctly, no matter how much the reagent
bottle is shaken. It masses together to the point that it makes
dispensing the solution near impossible - for it clogs the tip. This
kit is one month old.

The Tetra kit simply says NO3- on it. I have long ago lost the
enclosed pamphlet so I am uncertain which method it uses. The minus
symbol implies to me that the reading is nitrate-nitrogen.

And for an interesting aside, a Marine Enterprises Nitrate Test Kit
shows 0 ppm on the standard solution. Hmmm...

But, keep in mind that if your desired level of nitrate is 5ppm, that
would be 1.13ppm Nitrate-Nitrogen. Does the test kit go down to that
level? What is the lowest measurement value for the kit?

The lowest resolution on the chart on the Hagen kit is 5, although
using the sal****er scale could make it usable to 2.5 directly.
Guesstimation could extend this somewhat, but alas, the kit appears to
be completely inaccurate and inconsistant.

The Tetra Kit scale is 0 - 12.5 - 25 - 50 - 100.
Still unknown whether this is nitrate-nitrogen or Nitrate directly.

So the kits might be accurate after all, if they are reporting
nitrate-nitrogen.

If I understand this correctly, they are not.

I suppose that I could mix up various mixtures and use that to
calibrate/create my own scales for use with the kit until it is
expended... but is it worth the trouble?!

I happened to have these kits on hand, they were not purchased for the
purpose of testing nutrient concentrations. But the fact that they
are apparently inaccurate will steer me away from them in the future.

I will be on the lookout for more precise measuring kits.

Thanks again,

Greg
P.S. - Your web site is fantastic!