In order to assess the homogeneity of the mixture prepared in the tank, 60-mL duplicate samples were obtained at three tank depths: lower, middle, and upper. For minimal interference during the sampling process, a plastic probe (diameter cm) was attached to a 100-cm long rigid plastic rod that was marked at 5-cm intervals. Samples were collected by placing the rod on the tank bottom with the probe end attached at the desired depth. A syringe attached to the probe at the water surface was used to aspirate the sample. The first aspirated water was discarded to avoid contamination with water from other levels.