MH distance from water?

Toadfish · 07-24-2003, 12:57 PM

OK I got my 2 150w MH's for my 75g. I have the lights 8" above the tank. The light penetration seems minimal. Would it be alright if I dropped these down a couple of inches, to say 6"? Also regarding the shimmering effect that the MH's give off, Is it possible to get too much shadow thus reducing the light consumption? Everything looks good in my tank. Since I am only running the 10K's w/o actinics for now, the coloration has a yellowish tone. I can tell that my acro's and clams look healthier than under the PC's but the tank isn't as bright. I'll be recieving my 20K's within the week so I will hold off on the actinics for now.

Doug1 · 07-24-2003, 01:11 PM

What kind of reflectors are you using? 175's on a 75 should be bright at the bottom, esp with a DSB. Decent reflectors, like Spyderlight can make a lot of difference.
FWIW suposedly the orientation of the nipple on the bulb may affect the output, do a search MH or maybe someone can explain that better.
As a rule the higher the Kelvin rating of the bulb the less PAR and the bluer bulbs wont look as bright as say the 6500K Iwasaki. I like the Iwasaki /VHO act combo, lots of usable light, looks good to me and you can do dusk/dawn effect

Toadfish · 07-24-2003, 01:18 PM

These bulbs are 150w double ended. Man it's a strange setup. I don't know what type of reflectors are being used. It's all Tawaineese made stuff. I thought I would give it a shot since these folks are new to our area.

Prismaco · 07-24-2003, 02:38 PM

I have mine about 3" from the top of the water...

-Paul

ldmk · 07-24-2003, 04:05 PM

Quote:

Originally posted by Prismaco
I have mine about 3" from the top of the water...

-Paul

That's a little risky - if you have any jumpers or accidently splash a bulb while cleaning you could have it explode

On the other hand if you have pendants with a shield that's probably all right.

K.M.

07-24-2003, 07:18 PM

i have a glass cover so i know not as much is getting through but i have my 175's 4" from the surface...

kram138 · 07-24-2003, 08:36 PM

The LFS next to me has a large 100gal holding bin for their hard corals. They keep two 250w MH pendants about 3 feet above the water surface. The corals themselves are under about 6"-8" of water. They look great and I have never really seen any "sick" looking specimens. Does the same apply for your home aquarium? Is the fact that the corals spend no more than a couple of weeks in these conditions have to do with there success? I'm not sure. I actually plan on hanging a 400w MH pendant about 18" from my 80gal hex. We'll see what happens.

asmith · 07-24-2003, 08:58 PM

Our 135 with 3X250 Mh lights are about 8" from the surface of the water with spider light reflectors. I don't see any reason to go lower. I don't want to splash them and blow the bulbs.

Andrew

Doug1 · 07-24-2003, 09:11 PM

Quote:

Originally posted by kram138
The LFS next to me has a large 100gal holding bin for their hard corals. They keep two 250w MH pendants about 3 feet above the water surface. The corals themselves are under about 6"-8" of water. They look great and I have never really seen any "sick" looking specimens. Does the same apply for your home aquarium? Is the fact that the corals spend no more than a couple of weeks in these conditions have to do with there success? I'm not sure. I actually plan on hanging a 400w MH pendant about 18" from my 80gal hex. We'll see what happens.

I suspect the short duration in holding staves off long term detrimental effects from low light , the shallow depth also probably helps, but long term I dont see it as a do able scenario for a home aquarium. Light obeys the law of incverse square so the distance from the animals decrease the light levels in a non linear fashion. think of it as the light wil be 1/4 the strength at 18" that it is at 9 " not half. Thats a simplified version, I dont do math
Hopefully someone more versed in physics will jump in and clarify that

laddy00 · 07-24-2003, 09:28 PM

Light loses intensity because it is spread ing out. I think that the lighting for that LFS is not bad because there is so little distance between them and the surface of the water. Water "absorbs" light much quicker than air.
Here is a quick link that explains the inverse square law (very simple to follow): http://hyperphysics.phy-astr.gsu.edu...orces/isq.html
I'll see if I can find the relationship for light absorption through a medium. It will most likely only be for a particular wavelength.

laddy00 · 07-24-2003, 09:29 PM

Sorry, them refers to the corals and their proximity to the waters surface

Buehlz · 07-24-2003, 09:37 PM

I know this is off the subject but I am picking up a 180 gal system in a couple of weeks... can anyone lead me in the right direction of finding somewhat afordiable lighting for this system?

Doug1 · 07-24-2003, 09:39 PM

cheapest dual and single 400w MH you can find

Geoff · 07-24-2003, 10:06 PM

my 400w iwasakis are 8 inches form the surface of the water. i would not go any lower than that. i get very little spray on the bulbs, i do not want to get any more.

it is spray not drops, so i am pretty safe.

Buehlz-one of my magnetic ballasts went on me yesterday. so i ran out to HD to see if they had any ballasts. i lucked out, i do not know if this is a store thing or not, but i picked up a 400w mh fixture for $30!!. i just wanted the ballast out of it. this was a tar ballast. they last longer, but are not as efficient. i care about longevity. if you can find some of these and then get some of the sockets and reflectors you can come out pretty good.

G~

Toadfish · 07-25-2003, 10:45 AM

Well...I moved my lights down to about 5 inches above the water surface. Huge difference! The fixture I am using has a glass sheild so Im not so worried about the spray factor.