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Re: [APD] KH question and pH crash
Bacteria seem to add a lot to the acidity through nitrification, er...
ammonification actually. Some bacteria create NH3 (well most respiring
organisms excrete NH3 in some way) but in the water the NH3+ ion quickly
bonds to free H+ ions to form NH4+. Now plants and other bacteria
consume the NH4+ along with O2, using the N as their energy source. The
bacteria in this case free some H+ and some H2O. They also excrete
again some NH3+ with converts to NH4+ in water the the process starts
When plants consume NH4+, they seem to go through a few processes to get
and use it. First, to bring in a + ion (cation) they generally have to
release a - ion (anion) so that they remain at a balanced internal pH.
This is often done using OH-, something they can fairly easily form
during the many steps of photosynthesis' light and dark reactions. Now,
at the same time the plants need anions like NO3-, PO4^3-, etc as
nutrient sources. To obtain these they must release + cations to
balance. Hence, they can use the H+ released from NH4+ assimilation to
bring in useful anions. Also, AFAIK, plants (especially submerged
aquatics) rely heavily on the internal flow of H+ to carry nutrients
around the plant. I forget what this is called but something streaming,
if memory serves.
Adding KOH to water, KOH will immediately fully dissociate into K+ and
OH- since it is a strong base. There are lots of other dissolve ions in
our water for those energetically attractive ions to bind to but I think
the OH will fairly quickly react with the H+ to give you water and the
K+ will float around until it gets used by a plant or until it finds an
anion with which it will precipitate. However, I cannot think of any
typical (-) charged ions K will form an insoluable ion with.
Disclaimer, the above info is gleaned from personal reading,not from
anything scientific and is recalled only to the best of my memory. And
remember, since to take something in, something opposite must go out- I
only retain half of anything:)
Jerry Baker wrote:
> gbooth at frii_com wrote:
>> From this it is clear why aquariums with low KH seem
>> unstable - as acid is produced by biological action, the KH is used
>> up; when it is gone, the pH is free to drop rapidly as H+ ions are
> I suppose the H in NH4+ (ammonium) has to go somewhere after the
> molecule is broken to make NO2-- and NO3- by nitrifying bacteria.
> However, if plants are absorbing the NH4 directly, what are they doing
> with it? Does it result in free H+ ions, or are all the atoms consumed
> in the process? A little KOH could be of use in the aforementioned
> situation. You get K without having to add some unwanted anion.
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