there's no definate answer to your question. what you want to do is look into the corals you'd like to have. If you want just soft corals and LPS (large polyp stony) corals, your lighting doesn't need to be as strong as if you have SPS (small polyp stony) and/or anemones. So your first plan of action should be to put together a list of corals you want. Do some research and then take it from there.
Now a MH is a great light, but that is the strongest one AND the most expensive. So if you only want corals that need moderate lighting, that might be a bigger purchase than necessary. When you see a coral that nees "moderate lighting", normaly a high amount of just PC lighting would do just fine. If it says it needs "strong lighting", that normally means you'll want VHO or better.
i just recently started my reef tank, and this was a question that i had too. I sat down and decided i wanted on of those tightly-packed reef tanks, you know where there's corals on ever inch of LR. Well, i went from there and did some research on the different corals. i eliminated all of the corals that'll sting nearby ones, and then narrowed it down to the ones i thought were most beautiful and compatible. I took a look at my list and realized that 95% of them just needed moderate lighting, so i went with a moderate-high lighting setup. I have a 55g, and i bought a outer orbit 4x96 pc setup. This is perfect for the mushrooms, zoos, and polyps i want, along with the other handful of corals. I eliminated the 1 or 2 corals i wanted that required strong lighting. I figure it's ok because there's so many corals i can get with the lighting i have.
so i hope this helps!!! do some research on the ones you think you'll want and take it from there.
