Hi - I have a 75G I want to put some T5 lighting for a reef tank. I'm thinking about a 4 light IceCap retrofit set. Could someone briefly explain the timers i.e. if I get the 4 unit set, it will come with one ballast that can only control the 4 lights on it? Is it necessary to get a second ballast to control two of the lights, and simulate the dusk/dawn effect? Or should all 4 just come on at the same time?