One more thing - ammonia is poisonous to plants as well as the fish. The
plants can only utilize ammonium, nitrites and nitrates.

NOt tottally true. The plants may only absorb Ammonium, and not ammonia(not
sure)...but even so, theres always an equilibrium between the two, so if the plants
are eating all the Ammonium, a lot of the ammonia will convert into Ammonium.

Rich