Temperature and mortalities were recorded daily, and pH , total ammonia nitrogen and nitrite were measured weekly with a Hach™ DR/890 colorimeter test lab in two randomly selected aquaria per system . Un-ionized ammonia was calculated from the results of the total ammonia nitrogen and pH measurements. Mineral concentrations in the water were analyzed as described for the diets. Hardness, calcium and chloride were higher in the MOD system than in the LOW system , and other water quality characteristics were similar between systems.