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Old 08-01-2011, 12:17 AM   #1
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36" reef lighting / MH question

A long time ago, when getting into the hobby, I bought a really sweet 48" fixture off ebay. When I got it, I found out the moon lights were on the same circuit the actinics were on so I sold it. That light had 2 MH pods, and they said you could put 150w bulbs or 250w bulbs in it.

Fast forward to now. I have acquired a used 46g bowfront on craigslist and I am getting ready to set it up. As I am looking at lights it has occurred to me that my tank has a center brace. This seems to be a problem as most 36" metal halide fixtures have a single MH pod...in the CENTER of the fixture Now if I could cut that center brace away with a dremel that would be perfect, but we all know that's a pretty bad idea, I think.

So I found this:
36" 3 ft Metal Halide T5 HO Light Aquarium Reef 656W | eBay

Now this sort of thing would be perfect for my particular tank, except WOW that's powerful. I don't want an algae farm, a 2k electric bill or a 95 degree tank, so here's my question (FINALLY!)

Can you put a double ended MH bulb of a lower wattage in a circuit that's rated for a higher wattage and have it work just like that fixture I had a while ago? Can I stick 150w DE bulbs or even (omg this would RULE) 70w bulbs? Safely?

If that could happen with the above fixture I'd be in heaven, and so would my corals. Otherwise I'm stuck with unattractive options like Viper clamp lights (that still don't give me actinics or moonlighting) or pendants (same issue). I really want an all in one solution, and both PC and LED fixtures are too expensive (in different ways). Any help would be appreciated.

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Old 08-01-2011, 02:25 AM   #2
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no you can't. a ballast is designed to put out the volt-amps it is rated for, puttign a smaller MH lamp will blow it up, putting a larger lamp in a smaller fixture will cause it to not start properly.

most MH ballasts have multitaps in them, meaning you can change the input voltage on them, 120v, 277v, or liek we have here in canada 347v. i'm an electrician and i work with alot of MH highbays (slowy going to fluoros) and my foreman decided when he was renoing his house to take one and beign the lazy dillhole he is he didn't bother changing the tap from 347v to 120v so the 400w lamp barely put out 70 watts worth of light, because the volt-amps of the ballast was not being put out. he eventually kileld the ballasts starter.

moral of the story, use the right ratings, so if its a 250watt, use a 250watt.

why not sell this MH fixture you already have and buy a 4 lamp t5 with individule reflectors. this way you won't block most of te light with the brack, and still be able to grow the same corals you would with a MH and you might have money left over from the sale to buy some high quality ATI lamps

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Old 08-01-2011, 05:42 AM   #3
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Thanks for the reply. Thought it might be a long shot but then again you can put a 25 watt household bulb in a fixture rated for a 100w bulb. I thought it might be like that.

I sold that fixture quite some time ago because it lacked the capability to do what I needed. I don't really want to use T5 or PC because a.) I want to keep the occasional SPS, clam or anemone, and b.) the cost of replacing those bulbs every six months gets pricey quick. what would be perfect is a 70 w MH bulb on either side of the bracket. To do that I may simply have to use a couple of Viper clamps, but I'd prefer the elegant look of an all in one fixture instead of two viper clamps, a PC actinic strip, and moonlights crammed where they can fit.
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