Define your user stories in terms of accuracy, temperature range, water surface details , update rate, output resolution and format
Then search Google and EDA for ultra sonic distance
The maximum range is 6 meters (your specification is 8 meters) and I do not think that without a suitable enclosure that the sensor will survive the humidity in the tank. The interface is I2C. The microprocessor must have an I2C capability (preferable HW). There is no internal temperature compensation