Nitrogen Excretion

An estimate of the nitrogen that will be excreted into the water can be empirically calculated by the following;
 Nw = NT - (NT X 1/FCR)
 where, NT = Total nitrogen added to the system
  Nw = Nitrogen excreted into the water
This is not exact as it does not allow for lipids and other nutrients in the diet which may be retained in the fish, but is a good estimate and errs on the side of safety.
See also Ammonia calculations