SPSJunky,
Since your tank is deep, but also skinny at 18" wide, I wouldn't be "in a hurry" to give short shrift to a 250 watt solution.
To begin with, 250w non-Radium DE's in dinky mini-reflectors are a wholly different proposition than 250 watt SE Radiums in real reflectors being run on HQI ballasts.
First, on straight wattage Radiums on HQI Ballasts run beyond the nominal rating - 270 watts or more per bulb in practice. It's a big difference if you see 250 watts side by side with 270+ watts. (
Radium.de - just for reference check the HRI/T-Aquastar bulb stats.)
Second, you will get a much better spread - better should mean
less spill in your context - from what's considered a full sized reflector.
Together, what this amounts to is more light to begin with and a greater percentage of the light making it into the tank - completely adequate for the tank depth in question. The disadvantage to this solution (if anything) is cost - of the third reflector and ballast and third bulb in the replacement cycle - but to me cost is out the window if you're considering halide in the first place.
FWIW, I really think the Radium bulbs are the biggest difference in robert's setups....though the better reflectors certainly make a big difference too. There's no reason that 250w Radiums wouldn't look just as much better in that setup vs the 250w HQI setup.
This does not address the coverage issue, however.
If you check out the advancedaquarist article linked in the post above, you will see that there is no reflector that gets around the point-source lighting that metal-halide is......the center is always most intense and the edges are always dim. There is a trade-off between how intense the hot spot is vs how dim the edge coverage is. I won't say that it's impossible to get adequate coverage with two 400 watt bulbs, but you may have a tough time IMO with the balancing act.
Depending on tank layout and what corals you ultimately choose, bleaching under the hot spots will be a real risk if you have to lower the reflectors enough to compensate for a lack of light at the edges. SPS at the perimeter not finding enough light to color up and grow well could be a risk if you end up having to raise the lights too much to avoid bleaching (not all corals can acclimate to the level of intensity you can have at the center). The reflectors are circular and the tank is rectangular of course, so light spill becomes a bigger factor the higher above the tank you go as well, wasting the extra wattage of the bigger bulbs. Getting reflectors that give more coverage also waste more light due to your relatively narrow (18") 150 gallon tank. Again, not necessarily insurmountable - especially depending on your tank layout - but running three reflectors will eliminate this concern almost completely. Over-lighting is almost an impossibility with the 130w less per bulb, while the overlap between bulbs provides more than adequate intensity at the interior lighting perimeters. If there was a reason that you *had* to mount the lights up higher, then the equation shifts decidedly in favor of 400w bulbs.
FWIW, I've seen 400 watt Radiums on electronic ballasts mounted in Coral Vue Lumen Bright reflectors mounted about three feet above an SPS system - the over-lighting issue is not made up. YMMV, but worth considering.
Some relevant stats that may be interesting.
3 x 250w + 4x96 = 1134 watts
2 x 400w + electronic ballasts = 800 watts
3 x 250w Radium + HQI ballasts = 810 watts
The watts here do make for a good apples-apples comparison, IME. First thing to notice is that no matter what there will be a reduction in light over the tank vs your current light, so a power savings will follow - over $100/year for a 10 hour lighting schedule. Second, with 250 watt bulbs and good reflectors you're putting down the same amount of light as the 400w solution, but in a way that's going to be a lot easier to manage and, overall, be more useful to your corals. (Unlike their other denominations, 400 watt Radiums are designed as power-savers, so are actually 360 watt bulbs.....electronic ballasts I believe will drive them to 400 watts in practice, giving a similar look to the 150 and 250 watt Radiums on HQI ballasts.)
At the end of the day, if you are going to make a change to running pendant lights there's not much harm in experimenting either way as I see it. If you're dissatisfied for some reason then it's a small amount of additional hassle to change it up and add (or sell off) one pendant.
You're sure that LED is off the table? ;-) Comparable GU10 LED setup: About $750 to build. (That's a skeleton fixture good for installation, similar to mine....finishing it for display or not is up to you and your tastes.) 410 watts -
another 50% less power use vs your Aqualight, saving you $260/year. No - zero - heat transfer to your tank. (You won't need a chiller if you do need one now.) Also no bulb replacements, saving you about $250 every six months. This fixture will pay for itself the first year.
-Matt
