I would most definately go with the metal halides in comparison to 6 60" T5 tubes. With two Nice pendants (like Reef Optix III's or Hamilton ReefStars) and two nice bright DE lamps (like 10KK lamps) you could easily cover 60" of your aquarium with light that I promise is bright enough to keep SPS and Clams on the sandbed in a 24" tall aquarium. You want to keep them horizontally closer to the lamps than further, of course. I personally don't think that 6 60" T5 tubes will be enough light to keep SPS and clams happily on the sand. 2 Halides like described above should end up costing about the same a 6 T5's (at least based on where I shop, and assuming you are going with the Icecap ballasts for the T5s and buying everything new
) and will draw about the same amount of power.
But if you are willing to go with 8 T5s or more then I would go for T5s. Check out these aquariums, both run on T5s alone
http://www.korallenriff.de/Mohr/
http://www.hausriff.ch/4534/108355.html
Both of these aquariums are 30" wide and 24" tall.
IN order to mimic something like the second link, and be able to keep clams and SPS on the sand you would want to go with 8 T5's. He runs 10 T5s over that 30" width, and is upgrading to 12 T5s. Notice in the first link that he keeps all of his light loving SPS Higher in the aquarium. This is because he runs 8 T5s over that 30" width, so there isn't enough intensity for these light loving corals and clams on the sand.
One important fact to keep in mind is that these people change their tubes every 6-9 months due to spectral shifting. They consider this very important and a tried and true method of success. The fact that you can have such a varied spectrum with T5s by being able to mix so many different types of tubes without losing a significant amount of intensity (when done properly) is what makes T5s so advantageous in comparison to Metal Halides. If the spectrum shifts then the benefits of using T5s is lost. MOre lamp changes = more $ in the long run.
Also see this American T5 tank
http://www.reefkeeping.com/issues/2005-03/totm/index.php
However, everything will thrive under metal halides alone. Throw 3 250W DE Pheonix 14KK lamps into 3 Reef Optix III's ran off M80 ballasts or into 3 Hamilton ReefStar Systems and I'm sure that will treat you well for years to come, and could end up saving you $. Metal halides hold their spectrum for longer than T5s, which eventually leads to $ saved. Certain lamps hold their spectrum longer than others, or so this blossoming new thread is attempting to point out
http://reefcentral.com/forums/showthread.php?s=&threadid=787010
Initial setup could cost about the same as 8 T5s, if you shop right. Plus, with metal halides you have a little less clutter to deal with in comparison to all of the uncooperative wires that are used for fluorescent lighting. And, IMO, it is easier to control the heat that is put off by Metal halides by using a simple high velocity fan and a open top system.
Soooo ... It appears that I may have just wrote on and on and not helped at all
. Ultimately it's all up to personal preferance. YOu will have success with both 8 T5s or 2-3 halides where keeping SPS and clams on the sand bed is concerned.
And most importantly, success isn't dependant on lighting alone, but that topic is far beyond the scope of this post
.
Sorry if I ended up making your decision harder or told you information you allready know or trailed on a little too much
. This Espresso machine I just purchased has me addicted to Iced Lattes and the caffiene just made me want to keep on writing. Anywho, good luck :thumbsup: LMK if there is anything I need to clarify or if there is anything I could help you further with.