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Re: [APD] Nitrite toxicity and GH

I believe Robert T. Ricketts wrote this email section below:

In a word, no.  Nitrate or nitrite play no role in General Hardness, and are
undetected by that test.  Unfortunately there is no available test kit for
us to detect chloride ion in freshwater.

That's odd.
The reason I asked was that there is a nitrite toxicity calculator test on the PFK site and on using it, it asks you for nitrite level, GH and volume to tell you where or not there is enough of the Chloride ion in the tank.

This seems to indicate a relationship between GH and hardness.


"This program calculates the level of NaCl required to raise chloride levels in the system to that at which the nitrite present can be detoxified, and takes into account the background level of chloride already present in the system."

A friend of mine has a small planted 30L tank with an oddly persistent level of 0.25 ppm of NO2 and a GH of 9

This calculator returns the above values with a result of :

"Research on the reduction of the toxicity of nitrite to fish has shown that the ratio of chloride to nitrite must be at a minimum level to be effective.

Your water already contains sufficient chloride to make the nitrite present less toxic to the fish, so we would advise conducting a partial water change and not adding any further chloride to increase the level."

(At present she is adding Prime to render the nitrite non-toxic.)

But yes, chloride ion does block nitrite toxicity in freshwater fish, by
competitive inhibition - competition for the binding site on the hemoglobin

This was how I understood it too. :-)

I have seen recommendations as low as one-tenth teaspoon per US
gallon (from the Skeptical Aquarist), but I have used significantly more -
but still quite low dosage - at one quarter to one-half teaspoon per US
gallon without problems.

Thanks for that Bob.

If you are concerned with the sodium ion, potassium chloride will have the
same effect as would ordinary salt (sodium chloride).  Potassium chloride is
the material in many salt substitutes available from the grocery stores.


Stuart Halliday
200 Million years in the making...
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