He will grind the rock around him to accomodate his size when he grows. I am sure he will do just fine as long as you keep him well fed.
IME, I tried DT's, but found Tahitian Blend to provide much more stable and positive long term results in the smaller clams. My smallest maxima was at best an inch when I got him, more then double that now. All on 150W DE and daily Tahitian blend.