Nice set up. One tip, your alli will feel more secure (happy) if you add lots of drift wood that is close in color to his shell. Right now, he sticks out like a sore thumb on that light colored rock and he knows it. He's an ambush predator and needs to blend in with his environ to hunt. Over time, he may become slightly closer in color to whatever is around him, but that particular combination is a pretty big stretch to ask of him. Good luck with him.