Twin Alternating Softener Logix Performa Controller

Twin alternating softener Logix performa controller. One master head and one slave(dummy) head .

The master head contains the settings and controls both system's backwashing/regeneration. It makes sure one is always operational at all times.

Backwash's itself on a volume based regeneration. The capacity between regeneration's is set by the settings imputed into the controller. 

Please advise what size tank the valve is for so we can set it up correctly and connect the proper parts.