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Re: pH VS ammonia
I think it is also important to point out that the chemistry that is going on
in the main tank may not match the chemistry that is going on at the gill
surface of the fish. It is to the gills that ammonia is most harmful and there
is certainly a much different chemical environment within 1 or 2 microns of the
gill membrane then out in the tank proper. The equilibrium concentration of
ammonia in the main tank is most likely irrelevant.
john
On 09-Mar-01 Wright Huntley wrote:
> 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
>
> http://www.atchison.com/Killifish/BAKA-WCW-10.html
>
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E-Mail: John N. Alegre <listhub at libros_andante.mn.org>
Date: 09-Mar-01
Time: 13:06:49
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