Prompt operational response to abnormal conditions is critical to ensure treatment plant performance and compliance are maintained. Laboratory data is critical to ensure proper response is taken. Availability of laboratory staff and the time requirements of the laboratory analyses can cause delays in providing needed data for prompt response. This paper identifies simple diagnostic tests that can be performed for three common, abnormal conditions in a wastewater treatment plant: high chlorine demand due to nitrification-related conditions, floating sludge on the secondary clarifier, and potentially toxic substances in the raw wastewater. The tests can be performed with lab equipment and supplies that are common at wastewater treatment plants and available to operating staff.