I am still debating about my lighting... I have a 90gallon tank wiht a full hood so whatever kind of lighting it will be retrofit. I will have a 4+" DSB so the tank will end up about 19-20" deep with lights 4-7" above. I plan to have mostly LPS and SPS but wouldn't mind being careful of placement with any specimens of particular high light needs. I'm not really interested in clams. Also any lighting I think I will put an acrylic shield below the lights for easy cleaning and to keep to minimum the condensation on them.

Full T5
I was thinking about starting with 6 T5 (4' 54W each). If I do 6 T5 there would be room to upgrade to 2 more at some later point. I'm guessing my actinic period (2 bulbs) would be 12 hours and a 10 hour period for the other 4 bulbs (one actinic and three daylight). I could always upgrade from the t5 to MH at some point later on and just sell a couple of the T5 kits (I'd need to keep one for actnic anyway).

MH plus T5 actinic
However I am now considering MH and T5 for actinic. I'm not sure about the HQI or single ended option but don't see any particular reason to go either way. I do understand the difference. I may lean toward a single ended if I do the acrylic shield anyway. I am also not sure about the wattage. If I do 150W I think I would run them for 8 hours. If I did 250W I would prefer to limit the daylight period to 5 hours (though I might stagger the two lights slightly). 175W would be 7 hours I guess. I am a little concerned about the heat from MH bulbs, especially the higer wattage. My tank room could easily hit 75F in the summer afternoon and may occasional approach 80F. Are a couple little fans enough to cool these lights/tank in a full hood (open in rear)? I do enjoy the shimmer but that is not enough to get me to spend more on electricity. Is 2x250W for 5 hours enough for SPS?

Please share you thoughts and comments on the different bulb choices and what might be best for my setup. My primary goal is adequate lighting but close second is economy. That includes bulb replacement and elecricity usage. But I will invest a little more at startup for a better solution. Of course all that said keep in mind LEDs could soon be more reasonably priced and I could be replacing with those in 1-3 years. Since that seems to be adequate light and definitely economical to run.

Thanks!

Also forgot to mention...

In a MH world, I'm leaning toward electronic ballast for efficiancy, size, and heat. Though I did see some relatively compact magnetic ballasts also; do these end up needing a fan on them or something? I want to mount all ballasts to the back of my canopy.

My MH would be 10k.

Also I am interested in hearing about any bulbs, ballasts, or retrofit kits that you have experience and an opinion on.

I'm in the same boat as you trying to navigate through the wonderful world of lighting your reef tank.

I voted for 250's since I plan to put them in my new setup. I also want the electronic ballast and double ended. I will prolly be mounting pendants in my canopy.

Look into getting Icecaps for the ballasts- I always have read great things about them.
For bulbs, XM comes immediately to mind, but I'm not 100% sure on that yet.
Definitely have a few fans in your canopy. All lights going in a canopy need a fan in my opinion. I have no plans of using a chiller so I will blow the AC out of this house if I have too. :D

I will be tagging along here ;)

Right now I am leaning toward the 175W MH. It is almost no more cost than 6 T5 and the regular magnetic ballast is much cheaper than eletronic one.

I guess my biggest issue is woudl the reduced daylight period be adequate with the 250s? That route could actually save money because while the bulbs are a litte more, they also would last longer on a shorter period.

I have no plans for a chiller either, but I also do not plan to crank the AC either. I am a real energy miser. One thing that helps me is the tank is in the basement so not quite as hot as the rest of the house.

I think 175 shoudl be fine to start out at least. I'll also see what kind of heat those make and if i really think bigger would work unde rthe canopy without making too much heat. I could always upgrade from the 175 and use them on an extra tank or sell them or somehting.

Go for the halide.

i would say 250w halides. you could always add a couple of fans to the canopy to keep them cooler.

FYI ... 10k XM is one of THE best bulbs on the market, IMHO.