A Sodium Bicarbonate Dosing Methodology for pH Management in Freshwater-Recirculating Aquaculture Systems

Abstract

High-density water-recirculating aquaculture systems with hydraulic retention times above about 5 d must be monitored for alkalinity, and in the vast majority of cases, the alkalinity must be adjusted upwards to assure maintenance of desirable pH levels. Sodium bicarbonate is the preferred additive for increasing alkalinity because it is inexpensive, dissolves rapidly, and is safe for both personnel and fish. The high rate of carbon dioxide production in such systems requires significant stripping capabilities and dictates the appropriate alkalinity concentrations in this CO₂-enriched environment. The methodology presented for alkalinity adjustment uses measurements of pH and alkalinity to obtain an estimate of the system CO₂ level, which, in turn, is used to define the alkalinity concentration required to reach a targeted pH. A dosage table facilitates determination of the amount (g) of sodium bicarbonate to be added to reach the targeted pH for a variety of system sizes. The charts, which are designed for personnel with limited training, also indicate when additional CO₂ stripping capacity is dictated.