Stop! Please don't add a fish yet.
OK, I understand that your tank is 1 week old. So far, your water parameters (ammonia, nitrite, nitrate) are all low. That is about to change!
In the next 15 days, your ammonia levels will rise, until the bacteria that consume ammonia increase enough to consume it and change ammonia to nitrite. Then, your nitrite levels will rise, until a different type of bacteria increases enough to change the nitrite to nitrate. Plants (algae) consume the nitrate, or water changes can be used to keep it under control (10-20 ppm or less).
Most people will kick the nitrogen cycle by putting a small chunk of shrimp or tuna in the tank. When it rots, it creates ammonia. Adding a hardy fish, such as a damsel, will also work. But, 1) it may kill the fish or 2) you wind up with a fish that you really didn't want.
Take it slow. Read, read, read. Especially read the 3 steps to a reef aquarium.
http://www.3reef.com/aquarium-articl...ategory-1.html