Each barrel is 100 gallons, one of salt water (left) and the other of RO/DI (right). The salt water one is a flow through from the main display and connected to the house drain. I can take the tank offline with the closing of a valve then open another valve on the bottom and drain 100 gallons of old salt water in just a few minutes. I then transfer the RO/DI water to the tank on the left for mixing the new salt water. After the water is mixed I then open the valve and flow the display water back through flushing the new salt water through the system.
Very nice!