The effects of 12 bacterial amendments on reducing concentrations of total ammonia nitrogen (TAN), nitrite nitrogen (NO2−N) and organic matter in pond waters were evaluated in the laboratory. Concentrations of TAN, NO2−N and organic matter in untreated water (controls) naturally decreased with time during 16days. No large acceleration in nitrification or organic matter oxidation was observed from using these bacterial amendments. However, minor differences in concentrations of TAN and NO2−N, and rates of dissolved oxygen loss – an indicator of decomposition rate – were found between controls and treatments on some sampling dates. Compared to the controls, the bacterial amendment 5 at the manufacturer's recommended dose resulted in lower TAN concentrations on days 8 and 12, less NO2−N on days 6 and 8 and less oxygen loss on day 1. Water treated with the bacterial amendments 3 and 10 at the recommended doses had slightly lower TAN concentrations on day 0 (soon after initial treatment) and day 16, respectively. The bacterial amendment 11 at the recommended dose lead to lower NO2−N concentration on day 12. Organic matter in water treated with the bacterial amendments 8 and 10 exhibited a greater rate of microbial respiration on day 16. With higher doses or more frequent applications, there was lower (P<0.05) TAN concentrations in water treated with the bacterial amendment 11 on day 0 and day 2. The bacterial amendment 10 at higher dose and the bacterial amendment 7 at more frequent applications than recommended by manufacturers had a small effect on oxygen rate loss on day 1 and days 7, 9 and 13, respectively. The bacterial amendments 1, 2, 4, 6, 9 and 12 were not successful (P>0.05) at lowering concentrations of TAN, and NO2−N or oxygen loss rate on any sampling dates. Bacterial amendments are widely used in aquaculture in efforts to enhance water quality in ponds. This research showed no benefit of bacterial amendments on water quality in laboratory tests and doubts on the effectiveness of bacterial augmentation. •Twelve bacterial water quality enhancers were tested under laboratory conditions.•The products did not accelerate oxidization of ammonia, nitrite, or organic matter.•It seems doubtful that bacterial augmentation is a beneficial practice in pond aquaculture.