Skimmer. My wife has repeatedly stated that the most significant change she saw in how well the tank does was when I changed skimmers a year + a half ago. If the wife notices something positive from such a spendy item ... it's important
For flow, I'm preferential to something like a Tunze stream.
Low power use, far less heat added than a closed loop, and many are controllable w/ variable flow.
Beyond that - time and patience. I found my Acropora really took off after about a year of tank maturity ... I kept them before that, but color and growth were both weak in comparison with after IMO.
Good test kits for Calcium and Alkalinity ... and a method of supplying these two compounds to the tank. Many use kalkreactors, calcium reactors ... some with smaller tanks use 2-part [I do on my 58].
As for the substrate/methodology ... that's really your choice. There's benefits to both, creatures that IMO thrive a little more in one or the other ... and a million heated discussions on the subject.
Given success can be found through many methods ... find a way that works for your livestock, equipment ... and eventually, your husbandry style. It's not about being `right', it's about making your corals thrive
