Make sure the rock you are buying is fully cured before it goes in your tank and keep a close eye on your tang for any signs of ich, tangs are very prone to this and generally don't do well in younger tanks. I also would consider maybe bringing this one back as tangs are not a good beginner fish really and this one will grow too large for your tank. Also tangs tend to be very aggressive to any new additions, especially when they are added first and in smaller spaces. I would recommend you buy The Guide to Marine Fishes by Scott Micheal and The Consentious Marine Aquarist, they are full of good info. This hobby will only cause you headaches if you don't research any purchases before buying, almsot everyone here has learned this lesson the hard way.