A system for determining a quality (concentration) and a quantity (level) of a fluid in a tank, the system comprising: a first transducer configured to generate a first sound wave and to detect an echo of the sound wave, the first transducer positioned at the bottom of the tank; and a second transducer configured to generate a second sound wave directed up towards a surface of the fluid in the tank and to detect an echo of the sound wave reflected from the surface, the second transducer positioned at the bottom of the tank; a reflector positioned a known distance away from the transducer (115, 210), the reflector positioned such that the sound wave from the transducer (115, 210) travels toward the reflector; a temperature sensor configured to detect a temperature of the fluid; and a controller configured to produce a signal to drive the transducers (115, 210) to produce the sound wave, receive an indication of the detected echoes from the transducers (115, 210), receive an indication of the temperature of the fluid from the temperature sensor, determine the temperature-dependent speed of sound for an ultrasonic wave travelling through the fluid based on the time period from when the first sound wave is produced to when its echo is detected, and the known distance from the first transducer to the reflector, and to use the temperature-dependent speed of sound and the indication of the temperature to determine the concentration of the fluid in the tank, determine the level of the fluid in the tank based on the temperature-dependent speed of sound for an ultrasonic wave travelling through the fluid, and the time period from when the second sound wave is produced to when its echo is detected, and determine at least one of: (a) whether a contaminant has been introduced to the fluid when filling the tank based on whether a measured level of the fluid is out of range whenever the measured level exceeds the capacity of the tank; and (b) whether an error exists based on a dilution of the fluid being detected while a measured level of the fluid decreases. a first transducer configured to generate a first sound wave and to detect an echo of the sound wave, the first transducer positioned at the bottom of the tank; and a second transducer configured to generate a second sound wave directed up towards a surface of the fluid in the tank and to detect an echo of the sound wave reflected from the surface, the second transducer positioned at the bottom of the tank; a reflector positioned a known distance away from the transducer (115, 210), the reflector positioned such that the sound wave from the transducer (115, 210) travels toward the reflector; a temperature sensor configured to detect a temperature of the fluid; and a controller configured to produce a signal to drive the transducers (115, 210) to produce the sound wave, receive an indication of the detected echoes from the transducers (115, 210), receive an indication of the temperature of the fluid from the temperature sensor, determine the temperature-dependent speed of sound for an ultrasonic wave travelling through the fluid based on the time period from when the first sound wave is produced to when its echo is detected, and the known distance from the first transducer to the reflector, and to use the temperature-dependent speed of sound and the indication of the temperature to determine the concentration of the fluid in the tank, determine the level of the fluid in the tank based on the temperature-dependent speed of sound for an ultrasonic wave travelling through the fluid, and the time period from when the second sound wave is produced to when its echo is detected, and determine at least one of: (a) whether a contaminant has been introduced to the fluid when filling the tank based on whether a measured level of the fluid is out of range whenever the measured level exceeds the capacity of the tank; and (b) whether an error exists based on a dilution of the fluid being detected while a measured level of the fluid decreases. produce a signal to drive the transducers (115, 210) to produce the sound wave, receive an indication of the detected echoes from the transducers (115, 210), receive an indication of the temperature of the fluid from the temperature sensor, determine the temperature-dependent speed of sound for an ultrasonic wave travelling through the fluid based on the time period from when the first sound wave is produced to when its echo is detected, and the known distance from the first transducer to the reflector, and to use the temperature-dependent speed of sound and the indication of the temperature to determine the concentration of the fluid in the tank, determine the level of the fluid in the tank based on the temperature-dependent speed of sound for an ultrasonic wave travelling through the fluid, and the time period from when the second sound wave is produced to when its echo is detected, and determine at least one of: (a) whether a contaminant has been introduced to the fluid when filling the tank based on whether a measured level of the fluid is out of range whenever the measured level exceeds the capacity of the tank; and (b) whether an error exists based on a dilution of the fluid being detected while a measured level of the fluid decreases. (a) whether a contaminant has been introduced to the fluid when filling the tank based on whether a measured level of the fluid is out of range whenever the measured level exceeds the capacity of the tank; and (b) whether an error exists based on a dilution of the fluid being detected while a measured level of the fluid decreases.