Ammonia accumulation is a major constraint in freshwater aquaculture systems with limited water exchange, particularly before biological filtration becomes fully effective. Therefore, low-cost physicochemical buffering strategies are needed to control total ammonia nitrogen (TAN) under practical production conditions. To address this issue, the present study evaluated to the combined effects of natural bentonite and leonardite on ammonia removal and pH regulation in aquaculture systems. The experiment was conducted in a controlled freshwater batch system without live fish, where ammonia was generated from a single addition of commercial fish feed and consisted of eight treatment groups (B: 3 g bentonite, BL1: 2.5 g bentonite + 0.5 g leonardite, BL2: 2 g B + 1 g L, BL3: 1.5 g B + 1.5 g L, BL4: 1 g B + 2 g L, BL5: 0.5 g B + 2.5 g L, L: 3 g L, C: Control (no adsorbent)), each conducted in triplicate. Commercial fish feed containing 47.5% crude protein served as the ammonia source for all experimental setups. Ammonia levels generated from uneaten feed residues in the aquaria were monitored over a 12-day period. In this study, pH values decreased as the amount of leonardite increased. Considering the unionized ammonia (NH 3 ) limit values for fish farming, the limit values (0.05 mg L − 1 ) were reached in the control group on the second day of the study. This value was the similar in groups BL1, BL2, BL3, and L on day 8, and in groups BL4 and BL5 on day 9. The maximum NH 4 + concentration in the control group reached 45.4 mg L⁻¹, whereas the highest removal performance was observed in the BL5 treatment (0.5 g bentonite + 2.5 g leonardite), achieving 87.7% removal and an apparent adsorption capacity of 6.64 mg g⁻¹. Increasing leonardite proportion resulted in progressive enhancement of ammonium removal and a concomitant decrease in pH, which shifted the NH 3 /NH 4 + equilibrium toward the ionized form (NH 4 + ). The findings of this study contribute to the gap in the literature by presenting the first scientifically original data, showing that the use of leonardite, an economical and natural carbon source, together with the clay mineral bentonite has a positive effect on ammonium ion removal in freshwater aquaculture systems.
Öz et al. (Mon,) studied this question.