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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
>> generated.
> 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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