Ammonia's lethal concentration to kill half the population in 72 hours is 0.43 ppm ( source
http://www.ncbi.nlm....ps ammonia lc50 ).
Nitrite's LC50 is 345 ppm.
Nitrate's LC50 is 4453 ppm.
Because ammonia is generated from the degrading proteins in the fish flakes we add to the water (or in your case a rotting stick), and because it is so poisonous in such low concentrations, we fishkeepers have to be very careful about ammonia. There are two ways to keep ammonia at 0 ppm: either grow beneficial bacteria to convert ammonia to first nitrite and then nitrate, or grow plants that eat ammonia itself, removing it from the water column.
If you pick up some API Quick Start from Pet Supplies Plus, you would add all of the beneficial bacteria you need to instantly convert ammonia to nitrite to nitrate.
Info:
http://www.apifishca...ience_Sheet.pdfOr you could add some live plants. Info about live plants here:
http://www.theaquari...ical_FiltrationOne example of a fast grower is ceratophyllum demersum, a native of north america.
Basically, they eat ammonia very rapidly. Table two shows that they'll remove even 25 ppm ammonium (and thus ammonia, which it's in equilibrium with) in four hours. It would take bacteria three or more weeks to compensate for that ammonia. Plants therefore are good to have even if you only have one, because they're safeguards against ammonia spikes like if a fish dies and you don't notice.