[reeferaddict]

That's the key... keep an open mind... identify what you're going to keep, then what you'll need to do to keep them... one of the "dead trees" that I wish I had in the beginning was Tullock's "Natural Reef Aquariums". This book is excellent at explaining the planning all the way from simple practical systems to elaborate automated systems. By keeping your mind open and inquisitive you are already on the right track. If you have a question, post it on the board and watch for the different opinions... none may be right for you, but at least you'll have the experience of a half dozen or so other people to draw on before you proceed.

For your questions - 250W MH is plenty of light in that tank... keep whatever you want as far as light demanding species go. Actinics IMO are the KEY to successfully keeping corals. SPS growing near the surface may be the exception, but anything a few feet deep require light in the 420 nm range for their symbiotic algae to photosynthesize. Coralline algae DEFINITELY need it. I believe that if your MH light is from 14000 K to 20000 K you may not need to supplement with actinics as these bulb temperatures will provide enough 420 nm light waves. If I were you I would run your MH for 8 hours, having your actinics come on 2 hours before and turning off 2 hours after.

Running your MH all the time would be quite hot... but you won't really know until you try it... definitely mount some fans in the hood. A light that big on a tank that small may require a chiller. Will you be running a sump?

As for RO/DI, I bought a unit in the spring, doing straight DI for 6 months before that, and I would never go back. First off, you have total control of what goes into your water. There are so many good reconstituting/salt mixes that you can pretty much duplicate the important natural seawater (NSW) concentrations and eliminate almost all your impurities. No worries about phosphates, silicates, etc. You will have battles with algae no matter what you do, and this is the beginning. Though I have heard of a few successes from people using tap water, I have noticed that almost ALL long term success starts with pure, clean water.

I don't think a Fluval cannister would work well for a refugium. How would you light it? A refugium is an area separated from the main tank that needs light to grow macroalgae, copeopods, etc. that aren't subject to grazers and predators. Usually a fairly low flow goes through the refugium to minimize disturbance.

While you're studying up, I also recommend you determine how you want to skim and create flow.