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Re: Ammonia vs. Ammonium being Ph dependent


I think all they are saying is that it's a continuum.  You always get
both, never just one or the other.  At pH above 7 you get gradually more
and more ammonia (NH3), while as it drops below 7 get less and less
ammonia.  The pH determines exactly what the ratio will be.

See a great article by Neil Frank over at


From this article, you can see that even at pH's of 8.5, the amount of
"ammonia" (NH3) is only 15% of the total ammonia+ammonium (presumably
meaning 85% is ammonium).  At pH of 7.0, less than 1% is ammonia NH3,
and at pH of 6.0,  0.15-0.25 percent ammonia. 

I think what's happening with the books is that they are trying to
oversimplify things in order to get you to remember "high pH dangerous for
ammonia poisoning".  And you have remembered, and are doing the "right
thing" in your tank, but the downside is that you don't get the whole

On a related note, I have recently been accused myself of not presenting
things on the Krib in "simpler terms" so that beginners understand them.  
The accuser at one point said I was doing a disservice by using things
such as graphs and statistical data, which is confusing.  At another point
(on another forum), he chastised me for mentioning that incandescent
lighting *might* work under some situations.  These things, he says,
merely discourage and confuse beginners.  I should just tell people "this
is how much light to use in your tank. Don't use incandescents.  They're

There's always tradeoffs.  You can guess on which side of the fence I
stand. :)

    - Erik

On Thu, 10 Dec 1998, 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. I have encountered
> this information from more than one book and the writers have been doing us
> all a great diservice should this be proven wrong.
> Susan Romano
> ------------------------------

Erik Olson
erik at thekrib dot com