There is nothing wrong with either of them, they both have different effects and depends on what you really like. T5's can be overdriven with the Icecap ballasts with a wopping 80-90 watts per bulb on a 48". T5's will penetrate I believe 30" and there doesn't seem to be any problems with any corals or clams with high light requirement. I have seen some beautiful pictures of tanks on here that are SPS dominated tanks (if that tells you anything). You might consider moving the light about 6-8 inches for better success from the top. Be sure to climatize your corals when adding new light or bulbs, either will egg crate or gradually moving you lights closer every other day till you have the light where you want it to prevent stress or even worse bleaching corals. You can get great color, dusk to dawn effect and growth out of the T5 but minus the shimmer effect that the metal halide will give you. I think there will be less heat output and less energy consumption from a T5 than a metal halide. You could probably run a 60" by probably 6-8 bulbs over a 180gal, 36" side by side or run 3-4 halides. I really like the choice and technology in the t5's but metal halide have been around a long time and have lots of success. As you can see I'm leaning toward T5's but it's all preferance. Just do your research and look through the lighting forum and check out pictures of the tanks and what others have replied. There is alot of info on here, it's hard to get responses sometimes because there are so many of the same questions. Your better off looking through the forums and seeing what other have said unless you want to wait around for a reply. Good luck, it's a wonderful and expensive hobby but well worth the time and money. I can't stress enough to do your research before you make a purchase. Also you can save some cash here and there if your handy, ck out the DIY forums...lots of great stuff and ideas.
