Standard Controller 

A series of WaterFarm modules can be interconnected with a General Hydroponics Standard Controller, supplying nutrient solution automatically to all the units at the same time. Even if different plants are growing at different rates, each will be kept at the optimum level. 

The ideal nutrient level is maintained in all the interconnected units for days or even weeks. Another plus is that the Standard Controller provides the higher volume of nutrient solution needed as the plants move into their rapid growth phase - no need to replant into larger containers.

A 13-gallon master reservoir filled with nutrient solution is positioned on top of the float-valve activated 8-gallon Controller. As the plants draw nutrient from their individual reservoirs, the Standard Controller's level drops, causing the float valve in the Standard Controller to open and draw fresh nutrient from the master reservoir.

The Standard Controller can manage as many as 8 WaterFarm or PowerGrower modules.

If you need to supply a larger number of growing units, check out the larger sized Texas Controller.

More info from the Manufacturer (PDF format - Lots of detail.)