#WelcometoR2R! Either a gyre or a powerhead could be a reasonable solution depending on what you are trying to accomplish. Do you need general flow, do you need to stir up detritus from collecting behind the rockscape, or is there another purpose? Additionally, what type of coral(s) do you keep or are planning to keep?
I was looking for general flow for a mixed reef. I currently have a bunch of zoa frags a duncan with 6 heads and a couple leather corals I plan to stock the tank with some beginner sps in the future and some more LPS