One thing I would add about switching to a sump or wet/dry type filter. The maintenence is ALOT easier....
I have the same canister filter on one of my tanks, and I dread having to mess with it when it comes time for cleaning. I also like that with the sump you can move the rest of the junk out of the tank into the sump.... no heaters or skimmers or hose messing up the view.
You do have alot of fish in your tank....I am not one to talk about overstocking so hey if it works for you go for it, but I am sure extra filtration would not hurt. That being said IMO
I would think you have decent filtration with that much rock and the eheim and a decent protein skimmer.....assuming you don't have alot of messy eaters, which I would think not since you are talking about corals.
Good luck and have fun