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Re: pH VS ammonia
George Slusarczuk wrote:
>
> Hello,
>
> I just have to jump into this discussion. This is a good example of
> chemical equilibrium at work:
>
> As the unionized ammonia (NH3) is removed -- by ANY action -- the
> equilibrium will shift and more unionized NH3 will be produced, to keep
> the ratio ammonium:ammonia (NH4+:NH3) constant.
>
> So, as the NH3 is being continually removed, all ammonium will be
> converted to ammonia -- and removed!
>
> One thing of practical importance that we don't know is how FAST the
> ammonia will be removed, thus how fast the water will be detoxified.
Absolutely correct! Except the equilibrium is highly pH dependent. The rate
of getting rid of ammonia goes essentially to zero at about pH 6.5.
We know, as a matter of practical fact, that large bursts, like released
from thiosulfate breaking up 3 ppm of chloramine, are not dissipated quickly
enough and that many fish have died.
We also know, from long-standing practice, that more water changes are
needed if our biofilter is sluggish or inoperative and we have no plants.
The stuff builds up a *lot* faster than it dissipates, in a tank of baby
fish. "Change more water," as Charles says.
[I keep lots of plants around, as the faster-growing ones are particularly
good ammonia sponges when actively photosynthesizing. You should see the
colors on my ammonia-hating and oxygen loving *Procatopus aberrans* now that
I'm injecting CO2 into their tank and the plants are pearling oxygen
bubbles.]
Would it be a valid test to take an ammonium-containing fertilizer, in a jug
of RO, up to about 5 ppm, and then aerate while monitoring how long it
lasts? I don't think so. How does one neutralize the other half of the salt,
say the NO3- from ammonium nitrate, so it doesn't skew the pH and stop the
process by becoming nitric acid. Every NH4+ ion must lose a hydrogen to
*something* to become an ammonia (NH3) molecule.
I think that getting rid of the ammonia might consume a lot of whatever
alkalinity is available (another equilibrium at work), in non-RO water, but
then maybe create a bit of an acid crash as it comes to a screeching halt?
If we start with ammonium hydroxide, the pH will be so high that all we have
is ammonia, and it will go away really, really fast (ever breathe that
stuff?).
The short answer is that the equilibrium is inherently self-stabilizing by
reducing ammonia toward zero as the ammonium releases hydrogens. The
dissipation rate should be quite dependent on what other buffers are present
and in what amounts, and pretty unpredictable, as a result.
The good news is that any aerating, say, to drive off ammonia is making
things better for the fish by sending ammonia toward zero when that pH
drops, even if the dissipation has also stopped.
Getting rid of ammonia is considerably less trivial than I thought, when
this discussion started. Charles, is it time for you to jump back in?
Wright
--
Wright Huntley, Fremont CA, USA, 510 494-8679 wright at killi dot net
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