Re: [APD] NO3

[David Marshburn <marshbur at cs_unc.edu>]

Stuart Halliday wrote:
> So in theory by adding ammonia drops to my tank, the plants would only 
> take up the ammonium part and leave the free ammonia behind?

sort of.  free ammonia and ammonium are in some equilibrium, depending on 
pH.  as plants pull out the ammonium, some of the free ammonia will shift 
to ammonium ion (and i suspect that the pH will be affected).

here's the first article on ammonia/ammonium equilibrium that popped up on 
google, and it seems pretty good, if maybe a bit mathy.
http://equilibriums.beggiatoa.com/ammonia.htm

notice that, in order to go from ammonia to ammonium, the ammonia had to 
snag an H+ from the water, leaving a free OH- hanging around (this is why 
ammonia solution is considered basic).

also, the relative fraction of ammonia and ammonium is affected by pH.  at 
pH of 9.24, it's a 50/50 split.  at higher pH, there will be more ammonia; 
for "most" (?) planted tanks, the pH is closer to neutral, so most of the 
ammonia is in the form of ammonium.

this calculator will tell you how much ammonia vs. ammonium you have, 
based on total nitrogen concentration, pH and temperature
http://cobweb.ecn.purdue.edu/~piwc/w3-research/free-ammonia/nh3.html

-david
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