What has been your single best investment in a piece of gear for you'r tank that you could not live without? A certain skimmer? ATO? Reactor? Controller/ what part of the controller? Pump? An additive? Also Post the worst purchase you have made. My best is the wall plug timers that turn on and off. The worst is a Aqueon HOB filter that a guy at the lfs(***mart) said i had to have to have a successful reef tank...