YALQ (Yet Another Lighting Question)

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gear-head

Aquarium Advice Freak
Joined
Apr 30, 2004
Messages
261
Location
Central Pennsylvania
Perplexed about something :?

I have a 55g tank, 48" long, 20 something inches high.

I see rules of thumb for reef tanks of 3-5 watts per gal.

I see PowerCompacts from CustomSeaLife and others with 4x96w bulbs, for a total of 376 watts, or 6.8 watts per gallon, way above the rule of thumb.

Yet everywhere I read that you must have Metal Halides for a reef tank.

So is it the spectrum of MH that is required for reef tanks, not watts per gallon?
 
No, it's just that MH has dominated the reef hobby in terms of lighting for 20-30 years (at least). PC fixtures are relatively new, and in the past year I've seen companies double the number of models they produce, so they can cover freshwater planted tanks, and saltwater tanks.

It's all about spectrum AND intensity. MH is nice because you get 250watts out of a single bulb. However I know that with FW tanks, MH doesn't give off the most ideal spectrum. In a SW tank I don't know if it matters as much, since you don't have plants with chlorophyll that need high peaks in red and blue spectrums.

Also, from what I've learned so far, 3-5wpg is the 'minimum' for a reef tank. at 4wpg you're supposed to be able to keep most soft corals. definitely over 5wpg for the stoney corals.

I don't think a 4x96 fixture will fit a 55gallon tank. I'm pretty sure that fixture is 6 feet long and has 2x96 on each side..basically made mroe for a a 120gallon tank.
I bring this up because on my 75gallon, which is 48" long, but 18" wide instead of 12" like your 55g...I'd be very hard pressed to get 3 bulbs over the tank, with reflectors, front to back.
 
Yet everywhere I read that you must have Metal Halides for a reef tank.

Thats some old literature. Of course there are some things that will benifit greatly from the intensity that MH bulbs provide. ANother aspect is the WPG calculation does not hold weight with talking about MH bulbs because the MH light is only good for approx 2' sq. Beyond that the intensity drops off significantly. You would get better results from two 96W PC bulbs on a 48" tank than you would from 1 175W MH bulb for example because of this.
 
malkore, the bulbs are 3' long but they could also be set so they overlap. Although I have an 80 gal tank thats basicly the same size of a 55 just 2' longer and its a tight fit to have two 96W PC bulbs side by side with reflectors. If the reflectors where removed then I could see how you could get 3 bulbs inthee but four would make it really tight to where they are almost touching.

Another alternitive would be 4X 55W PC bulbs. These are only 2' long and thus you could put two on either side of the center brace. Other options would be 4' long VHO bulbs. YOu could get two of them over the tank at 110W each.

Its not the specitrum of MH that makes them unique over florecent bulbs. its the intensity.
 
The unit I was looking at was:

Current USA Orbit
48.75" x 12" x 4..25" without legs
(with legs the light is 6.25" tall, 12" front to back, and can adjust to lengths up to 49")

(2) Dual Daylight 96W and (2) Dual Actinic 96W

(2) 3" fans
 
This one?
http://www.marineandreef.com/products/Orbit-Dual.jpg

I don't like the looks of it. It looks like they've angled the bulbs in an arc, instead of being all horizonal, in a strip arrangement. I can't think of a reflector that could work properly in there to minimize all the restrike...so I think you'd be wasting a lot of the intensity (due to restrike).

I dunno though..it might not be that bad.
I'll just be making another canopy for my tank, and getting an AHsupply.com kit which has wicked reflectors.
 
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