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Ammonia Toxicity


  1. rising pH and ammonia
    by Randy or Deb Carey <carey/> (Tue, 03 Feb 1998)
  2. Ammonium/ammonia
    by "A. Inniss" <andrewi/> (Fri, 11 Dec 1998)

rising pH and ammonia

by Randy or Deb Carey <carey/>
Date: Tue, 03 Feb 1998
To: apisto/

Steven J. Waldron wrote:

> Ed wrote:
> >One wholesaler who was also an avid hobbyist had told me that he
> >believes that sometimes apistos that are shipped in bulk, and that are
> >at some point exposed to higher than 7 ph, may have had their gills
> >damaged by ammonia.  The ammonia takes on a more deadly form when in
> >higher ph water.  The fish start dying off in the next couple of days
> >and nothing seems to be able to save them.  I've purchased 30+ fish at a
> >time and watched them die off one by one.
>  I've seen this time and time again. I do not know about the correlation
> between high ammonia levels and high pH. Apistos oten get over packed when
> exported out of S.A. They often come in with extensive gill damamge from
> high ammonia levels.

Nontoxic ammonia ions (NH4+) disintegrate into toxic ammonia molecules (NH3) as
the carbonate hardness/pH rises.  An aquarist/chemist friend of mine illustrated

So as fish are tightly packed, the pH drops and the ammonia from all the fish
quickly assimulates into ammonia ions:  NH3 to NH4+.  Note that the extra
hydrogen of acidic water is available to attach to the ammonia molecule.  Add
harder, alkaline water to this
aged water and a steady chemical shift occurs.

As the water shifts to alkaline (high in hydroxide ions, HO), the hydroxide
rapidly receives the extra hyrdogen ion from NH4+ making it  NH3.  The suddenly
high concentration of ammonia in the water quickly diffuses into the fish cells.
(The charged HO4+ can't enter the cells.)  This rapid diffusion can cause ammonia

There's a little more to it than that, but that is the kernal of what's

Five years ago I was experiencing sudden "intoxicating-like" deaths of young fry
within hours of making 10% to 20% water changes.  If I transferred them to aged
water, the symptons would stop within a half hour and the fish were fine.  I was

Then I read an early 80's article in TFH warning that slight changes in KH
(Carbonate hardness) is fatal to young barb fry.  Bingo!  My tap water reads 14
degrees KH and jumps to near 8 pH within hours.  I adjusted my water changing
strategy and had success with species that seemed to die after my first water
change.  My guess is that fry, having smaller body mass, can't handle the sudden
absorption of ammonia as readily.

Only recently have I learned the reason behind this KH problem.  What surprises
me is how little I see about this phenomenon in aquarium literature.  So, my
friend and I are planning to collaborate on an article from my experiences and
his chemical background.


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by "A. Inniss" <andrewi/>
Date: Fri, 11 Dec 1998

	Hi Susan etal.  I just wanted to mention that cycling a tank at a
pH below 7 is not necessarily safer:  while it's true that relatively
non-toxic ammonium predominates such pHs, nitrite toxicity _increases_ at
lower pHs.  Why? Because nitrite and nitrous acid exist in an equilibrum
similar to ammonia/ammonium.  Nitrous acid predominates at pH below 7 and
is much more toxic than nitrite, because it is non-charged and therefore
does not require ion-transport channels, its passage through the gill
epithelium is not inhibited by competing ions (such as Cl-) etc. 



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