How high are your MH's?

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How high are your MH's?

Postby Guest » February 20th, 2000, 10:19 pm

Hi Beemr:
My favorite autos! We recommend to our customers that you build/buy a canopy that is a minimum of 12" tall (measuring the outside). This will put the bulb approx. 7-8 inches above the surface of the water. If your canopy is any lower, that bulb will really heat up the water, and you'll get much more salt spray on the bulbs. Again, this recommendation is for MH systems in canopies. If you're putting a tank in a wall, you have more flexibility because you can put the lights at any height, and not have to worry about the aesthetics of the project. Usually, anywhere from 7-10 inches above the water is a good height for the bulbs. This height is good for any of the wattages. You can put the bulbs 3' high if you want, but obviously you'll negate some of the benefits of whatever bulb you're using. You didn't say what size tank, nor if you're using a canopy, or if it's going into a wall; thus, I've given you a broad answer. HTH - Staff
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How high are your MH's?

Postby Guest » February 20th, 2000, 10:31 pm

I;m gonna put 2x400w 6500k and 2x110w VHO Actinics about 10-12 inches from the water in about a week. Waiting for this hood is worse than waiting for Christmas when I was little.....
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How high are your MH's?

Postby Guest » February 20th, 2000, 11:23 pm

I have a 175w 10k german halide with two actinics about 8" from the surface of the water.

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How high are your MH's?

Postby Guest » February 20th, 2000, 11:53 pm

Thanks for the replys.
I asked the question because a couple of people said they were putting Mhs 3" off the water--which was quite different from what I have observed.
Anyone else?
b.
(not a beemer fan--just my initials-really Image )
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How high are your MH's?

Postby Guest » February 21st, 2000, 1:12 am

How high above the waterline do you place your MH lights? What wattage? Problems with water, fish hitting the bulbs?
thanks,
b.
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How high are your MH's?

Postby Guest » February 21st, 2000, 2:43 am

I really appreciate your replies. I'm actively researching different metal halides this week...I can't wait any longer! Unfortunately my canopy was made 7" about a year and a half ago when I thought there was absolutely no way I would ever NEED MH lights Image So my bulb would be about 6 inches off the water. How do I protect my bulbs from splash and what exactly is the effect of water splash? I don't really expect splash but obviously evaporation droplets. Any ideas?
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How high are your MH's?

Postby Guest » February 21st, 2000, 7:08 am

I have two light assemble's, the mh one houses 2 400w 10k's(just switch from 6500k) and 2 110w vho's. The bulbs are 10 inch's form the water level. This a unit I made and I have a strip of 1/8" thick tempered glass covering the bottom. Remember the surface temp of a 400w mh is around 800 degree's. The other is a unit that has two 110w vho's directly in front of the mh unit. This unit blocks any light from blinding everyone in my living room.

Bill
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How high are your MH's?

Postby Guest » February 21st, 2000, 8:05 am

I am also in the process of building a canopy for 3 400w MH's. If you put them 4-6 inches above the water line do you have an open tank or do you have lids? Or, do you put a sheet of glass under the MH's. Ant other suggestions would be great!!

Thanks again
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How high are your MH's?

Postby Guest » February 21st, 2000, 8:49 am

on my tank i run them at 8 inches and everything seems all right.But would like to hear more on this as i am in process of getting a 125 and will build my own hood.so let's hear more what is best height?Does it go by wattage say 400 has to be 12 inches 250 10 inches.How about 1000 watt Image
Jeff
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How high are your MH's?

Postby Guest » February 21st, 2000, 10:43 am

MegaD was one of the guys that I mentioned above that got me started on this thread.
And he and MedinceMan are correct--the height can greatly negate the amount of useful light availble.
I am starting to believe that the old "8 to 12" high recommendation came from (1)older bulbs were not uv shielded and this could have a negative effect on corals when placed to close and (2)the older bulbs were using a more delicate glass envelope-apparently the current bulbs are made of borosilicate glass, which is said to have a low thermal expansion rate.
Since both of these problems no longer seem to apply--why not put them low? Guess heat--but that is not a factor for me anyway. And I guess a fish hitting an 800 degree surface even for just an instant is not comming away unharmed.
I am not wedded to anything, heck I'd put them in the water if that turned out to be closer to ideal. Image
b.
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How high are your MH's?

Postby Guest » February 21st, 2000, 11:49 am

I keep my MH's about 8 inches above the water surface. One thing you have to remember too, is that you have to get your arms and elbows in there too, and if you have a large canopy where the bulbs are fixed, having them too close to the water may be a maintenance pain. Its up to you and your setup.

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My reef is a living creature, it is not an object that I own.
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How high are your MH's?

Postby Guest » February 21st, 2000, 12:30 pm

14" (175W)
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How high are your MH's?

Postby Guest » February 21st, 2000, 1:08 pm

Bmw I run mine about 4" above the water, which brings up a good point, I dont think the people responding with the bulbs that high have any idea just how much it destroys the effects of even using halides. I've had water spray onto my iwasaki's, snail plugged overflow on the old tank, the fan hit the water and turned into a outboard motor, wasnt pretty, but didnt hurt anything. As far as jumping fish, I've never experenced that problem. As far as heating the tank, that's a good thing for me, as the heaters dont run as often. 8" I would say is 4" too high, and 12" is WAY too high. L8r mega

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How high are your MH's?

Postby Guest » February 21st, 2000, 1:29 pm

Mega makes a good point. Also remember the inverse square law that applies to light intensity loss over distance. If you double the distance, you lose 4 times the intensity; if you triple the distance, it's 9 times. (Please note that I'm using "intensity" somewhat loosely here; I'm sure someone with a better background in the physics of light will correct me here!) Image

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How high are your MH's?

Postby Guest » February 21st, 2000, 2:23 pm

wow, 14" that's the worst yet, a single 96w pc daylight sitting 4" above the water, is almost 3 times as much light to a coral sitting 5" under the water! 14" is way too high, basically your wasting alot of electricity. at 14" your halide is getting 38 lumens at the coral, If you move the halide down to 6" your halide is getting 115 lumens at the coral, pretty scary isnt it.

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How high are your MH's?

Postby Guest » February 21st, 2000, 5:59 pm

I'm also planning a tank that will use 3 400 watt mh along with some actinics.How do you guys get acess to the tank with the bulbs so low?Do you have a hinged front door or does the top hinge up like a piano bench?Thanks,Bob

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How high are your MH's?

Postby Guest » February 21st, 2000, 8:20 pm

^ Image
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How high are your MH's?

Postby Guest » February 21st, 2000, 8:56 pm

I was bored today, and lowerd my halide 1", using sanjay's 400w 10kk halide test, 135 par at 18" I calculated my center acro, a a.nana was recieving 674 par at the tips, and, with the light 1" lower, he is now recieving 823 par, pretty scary what 1" will do to the light making it into our tanks! I calculated the nana recieves 353 par at the bottom, this is up from 309 par, his base is 11" from the water surface. I assumed my pfo reflector is reflecting 70 % usable par with these numbers, my halides & vho are now 3 1/2" away from the water, before I went to the trouble of lowering the mounting points 1", I researched the numbers to see if it was worth it, YUP, definitly was worth it, wife came home, and I got this responce "what the h*ll did you do to the tank?" L8r mega

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[This message has been edited by MegaDeTH (edited 21 February 2000).]
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How high are your MH's?

Postby Guest » February 21st, 2000, 9:04 pm

Once again, should you have anything between the water and the lights? ie...lids for the tanks or some kind of shield built into the canopy.

Thanks again
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How high are your MH's?

Postby Guest » February 21st, 2000, 9:12 pm

I wont run anything between the halide and the tank, it would cut down on the light, I've never had any problem with salt creep on the bulbs, I do have salt creep around the tank frame (acrylic tank) that's a total pain to clean every couple days. L8r mega

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