So I am going to be getting a new for reefing. I need a little input.

[FitoPharmer]

If you ran a 100G and a 200G exactly the same additives, feeding, bio load, and maintenance wise the 200G would cost a little less then twice as much to run. But there is also the factor of your own personal time. In a larger system it seems like everything takes longer and when things go wrong they can be a nightmare to fix relative to a smaller system. You can cut down some of the work by installing equipment like a semi automated water change system or a algae turf scrubber. Also IMO QT procedures become more important the larger your tank is since starting over or catching a fish out of a 200+ gallon aquarium can be a tonne of work.