I have recently purchased a 200 gallon aquarium and I have decided to go with t5 lights. I was wondering if I could get away with using a 48" fixture since the tank is 72 " long or do I need to get a 60" fixture or 2 36" fixtures ?
Depends more on the type of corals you are planning on keeping. Of course most SPS are going to require more intense lighting and generally do better with a full length lighting fixture. You could use a smaller setup if you centered it and avoided putting corals on the ends but then what's the point of having a six foot tank?