At this point, carbon probably isn't needed. Doesn't mean it's harming the tank, though--especially since you don't have corals in there right now. In reef tanks, I like running carbon--not 24/7, but once a week or so, to remove the chemicals released by fighting corals. In a tank with just LR, you can run it, but plan on doing more frequent water changes to compensate for any trace elements pulled out by the carbon. Most mechanical and chemical filters can reduce the 'good' with the 'bad', so it's a matter of finding a workable balance. Skimmers are the same--they pull out 'good' stuff we put in along with the 'bad' we don't want in our water.
I have some polyps and mushrooms (okay, just one, he was floating around the sump of the 120 reef, so we put him in my 10 to see how he'd do) under less light than that, and they are doing fairly well. The polyps are starting to multiply--they need to be relocated, right now are tucked in the back in a weird spot. The mushroom is attached to 2 empty snails shells, so is very portable--right now it's on top of the rock in the middle of the tank. Doing well--not as happy as the ones under MH, but looks nice.