An ammonia electrode and the nesslerization procedure of a water quality test kit were compared in measurements of total ammonia nitrogen (TAN) in standard solutions, well water, and water from various aquaculture systems. The electrode generally was satisfactory, the test kit less so—especially in water fertilized with animal manure. Distillation did not improve accuracy or precision of the electrode when it was used with raw water samples, but TAN concentrations were affected by interferences when water from some wells was analyzed without distillation. In general, the ammonia test kit should be satisfactory for aquacultural use, but in intensive-culture systems the performance of the ammonia electrode seems to warrant its higher expense.