A fluid treatment system, includes a pressurizable tank, a compressed air source, and a float disposed inside the tank, the float rising or falling in response to a level of fluid in the tank; and a float-actuated switch assembly connected to the float. The float-actuated switch assembly starts introduction of compressed air into the tank from the compressed air source. A purge valve may be provided to allow fluid to flow out of the tank during the introduction of compressed air into the tank. The float-actuated switch assembly may include a magnetic switch.