This handheld sludge blanket level detector measures solid-liquid interface levels in clarifiers, tanks and lagoons. It helps users to eliminate unnecessary pumping/dredging, to monitor sludge bed depth for regulatory compliance and prevention of carryover, and to create valuable level profiles. The Sludge Gun® uses high-intensity infrared light to locate both sludge blanket and overlying cloudy layer. It detects clear surfaces, and silt/sludge/biosolids in densities ranging from light flocs to thick blankets. For example, Model 10-LP detects clear liquid surfaces; high-power Model 10-HP excels at finding the level of sludge in murky lagoons.