Managing Ammonia in Fish Ponds

Ammonia in water is either unionized ammonia (NH3) or the ammonium ion (NH4). The techniques used to measure ammonia provide a value that is the sum of both forms. The value is reported as “total ammonia” or simply “ammonia.” (In this publication, “ammonia” refers to the sum of both forms; the specific forms will be referred to as appropriate.) The relative proportion of the two forms present in water is mainly affected by pH. Un-ionized ammonia is the toxic form and predominates when pH is high. Ammonium ion is relatively nontoxic and predominates when pH is low. In general, less than 10% of ammonia is in the toxic form when pH is less than 8.0. However, this proportion increases dramatically as pH increases (Fig. 1). VI PR December 2004 SRAC Publication No. 4603