I'm glad you posted this thread. We have an opportunity here to help you avoid obvious long term problems. Hopefully you take this advice with an open ear.
You have a Blue Tang, aka Hippo Tang, aka Regal Tang, aka Dori, more accurately Paracanthurus hepatus. In the wild, this particular species of fish reaches 75% of its adult size in the first year of its life. As adults they can reach 14 inches in length. This is important because when kept in a small aquarium fish are exposed to chemicals in the water which stunt their growth. Read carefully... we are NOT talking about ammonia, nitrite, nitrate, phosphate, etc. Even if you have perfect water "chemistry", the growth will be inhibited.
When a fish has a stunted growth rate, it does not develop properly. There is no question or random chance invovled in this discussion, your fish will get sick. Its immunity will begin to suffer and it will catch disease. The first sign is generally ich. At this point you will have ich in a reef system and your options for treatment will be minimal.
The point is, you can make a smart decision today and save yourself this experience. You need to return the Tang to your LFS and buy a fish of appropriate size for this aquarium.
Moving on... you purchases Sun Coral, aka Tubastrea. There are 2 problems here. First, this is an extremely difficult species to maintain, so hopefully you are prepared for the daily feeding challenges. Second, Tubastrea is a "hard coral". It has sweeper tenacles that reach out and attempt to sting other corals. Placing a hard coral in a heavily stocked small aquarium is going to cause problems, especially given the close proximity of placement that you have chosen based on the picture.
Now, all of this being said, you are new here. I have no idea what your experience level is, so perhaps you are prepared to quickly move these corals and fish into larger tanks. I am posting this thread for the reader as much as I am to bring your attention to these issues.
The tank looks nice, by the way. Good luck.
