Re: Ammonium or nitrate uptake?

> From: krandall at world_std.com
> Date: Thu, 20 Feb 1997 07:53:36 -0500
> Subject: Ammonium or nitrate uptake? 
> You're right, if you have measureable amounts of ammonium _or_ more than
> trace amounts of nitrate, your tank is not nitrogen limited, and adding
> nitrate will do no good.  The fact, however, that you _have_ measureable
> amounts of ammonia(um) is a sign of trouble.  In a fully cycled tank with a
> healthy biological filter, even without plants, there should be no
> measureable ammonia(um) or nitrite.  In a "fish" tank, you will see rising
> nitrate levels until water changes reduce it.  In a planted tank with
> strong growth, the plants often use _all_ the available nitrogen, and you
> never see the nitrate level rise either.
> Karen Randall
> Aquatic Gardeners Association

Thanks for your answer, Karen. In the meantime we came to the conclusion that
the ammonium testkit must give a false reading because the nitrates that I
add with the KNO3 are used up by the plants. After 2-3 days, a 5ppm NO3 
reading has dropped to zero. And I have some cyanobacteria problems which
also points to a NO3 limitation. I never had any nitrite readings so far. 
Strange though that my ammonium testkit says 
in the instructions that 0.2 ppm ammonium is a normal reading. I have a 
reading of 0.3 ppm. The tank is half a year old, has only a few fish, strong
lighting and quite a lot of plants. Maybe the testkit it too sensitive or 
measures something different. It's a JBL testkit. I don't know if it's
available in the US.

Thanks for your help. Andi from Munich, Germany.