Did you buy the coral that white? You need to move is down ASAP. You should always start SPS on the bottom of the tank and move them up over a period of time. For me, I do it over 3 weeks. With one SPS you probably wont need to add anything beyond water changes, but once you get more (trust me you will!), look into dosing Kalk in your ATO or two part via doser. bulk reef supply has great videos on dosing methods. Make sure your Alk, CA and pH are not only a the correct levels but also constant. Small fluctuations can quickly kill an SPS. Keep your Po4 at less than .03 and No3 at less than .05. Some people say that having a tiny tiny bit of each works best. Others who have ultra low nutrient systems does things like amino acids or other SPS "food"
Another bit of advice, do a lot of research on SPS pests/hitchhikers and how to get rid of them. Although I am very new myself, it seems like people spend soo much time learning how to best keep SPS as it relates to chemistry, they forget about other things that can kill coral, which in my opinion, is just as important.