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Re: Ammonia vs. Ammonium being pH dependent

On Fri, 11 Dec 1998, Susan Romano wrote:
> Karen Randall has taken exception to my book based understanding of the
> nitrogen cycle, whereby I have understood ammonium to be the form that
> nitrogen takes in an aquarium when the Ph is under 7 and that it exists as
> more toxic ammonia in a Ph over 7. When cycling a new tank in the past I
> have strived for a lower PH for just that reason. If this information is
> erroneous I once again invite the chemists to comment.

How about a geologist?

Karen (and others) were correct about ammonia and ammonium coexisting over
a fairly wide range of pH.  Just the same, keeping the pH below 7 when
cycling a tank is a good way to reduce the toxicity of the ammonia.

The original idea that ammonia is ionized below pH 7 and unionized above
pH 7 is a gross simplification of reality - the sort of generalization
that you will find in texts written to the technical level of the typical
hobbyist.  If you use the idea that ammonia is relatively non-toxic below
pH 7 and more toxic above 7 you won't hurt anything, you just won't be TC
(that's "technically correct").

Roger Miller