The effect of the hydraulic residence time (HRT) for the removal of aquarium waste, such as protein, total suspended solids (TSS) and turbidity were investigated by using a foam separator Protein, TSS and turbidity removal efficiencies were increased with the increase of hydraulic residence time. The optimum hydraulic residence time was 0.5 min, and the highest protein and TSS removal rates were $14.4;g/L{cdot}day;and;38.9;g/L{cdot}day,$ respectively. The tendency of turbidity removal rate and efficiency was similar to that of protein.