The tanks range in size from 30 to 5 feet in height. The carbon pellets are 2-3mm in diameter. They sit on the bottom of the tanks that are filled with water. The pellets settle very fast, so there is a very distinctive carbon level line in the tank. I need to generate an analog signal to measure the varying levels of carbon pellets in the tanks, while ignoring the water. I can do this on a point level, but have had little luck doing it on a continuous level. If anyone has any suggested manufacturers of a continuous level sensor that will just pick out the carbon, I would be extremely appreciative.