I have a JBJ 28 with 2 clowns and a royal gramma in it, but I'm looking to add one more fish. The tank is about 7 months old so I feel like I'm ready to add a fourth and last fish. Just need help selecting a species. My clowns tend to hangout at the top and back of the tank, and the royal gramma hangs out near the middle and in the central rock work. I'm leaning towards a bottom dweller, but I feel like him and the gramma may fight over the main cave so I'm open to suggestions. I also don't want something that will outgrow the tank because this is all I have at the moment. Picture below...