Zaphod,
After much reading and investigation, I believe that T5's will be effective on a reef like yours (I am putting togather a 90gl 24" deep tank w/T5s as well). I think, at this point, we must be mindful of the bulb combo and placement of the SPS and clams. I have the EXACT questions you do regarding energy costs and par.
Grim contributed heavily with great information regarding T5's in another thread. In short, the par readings that Grim measured, with appropriate bulbs, ballasts and reflectors indicate that we should be able to do what you are talking about and I am most assuredly going to try very soon. I belive that it is possible to run a T5 SPS tank with some clams as well. The clam on the sand bed will be the question to be answered...
Again I posed the EXACT question a while back. No one has claimed to have put a clam on the bed of a 24" deep aquarium with T5's. There were those with MH set-ups that stated their doubts. I think all that remains is to try it. I am planning a 5-6" DSB (therefore putting the clam some 20" +/- from the lamps) and will try exactly that, but will be prepared to move it up in the tank if need be.
On exact lights after much searching reading here and other places I think Aquatinics probably makes the best units for the price that I have found. IMHO
There is quite a difference in the par levels achieved vs. reflectors. He claims (Tom) to have had good success with SPS corals and T5's. At this point, I am convinced and I have ordered a unit from them. Great customer service. I will post in the future as to my findings, albiet some time from now.
FWIW
