Thanks for the reply Dave, much appreciated. I am tagging @robsworld78 as he owns the RoboTank and knows the most about the control box and @Ranjib as he is the head guru for ReefPi.We use a 3.5mm female stereo jack for the connection to the fixture. We are using a common ground and two control wires in the 3.5 connector wire to control the ballast.
Not sure on the ReefPi configuration requirements but if we can assist in the wire we will. We make an Apex wire and also a GHL wire to connect to their controllers.