MH light positioning lowest height.

[nasotang00]

What is the lowest height from the water that 250w halides should be. How bout 175w. This will be for a 72 inch 125g reef. I am thinking of only having 2 MH. I will have leftover PC's to compliment the MH's from another tank as well. I need this to know how to modify my current canopy. The canopy is only 8" high now but planning to add some height if needed.
Thanks all

 

[keitho]

well, i've been told to keep them as close as possible to the surface of the water (about 6"), but mine are at a height of about 9". it's kind of hard to cover a tank the size of yours with only two lamps if they are each only 4-6" above the surface of the water. as long as you mount them securely, i wouldn't worry too much about splash on the bulbs (other than the fact that too much salt on the bulb may filter out valuable wavelengths). i routinely clean my bulbs because the get splashed from time to time. other than the extra maintenance, it hasn't caused a problem. also, you may want to consider going with 250 watters or even 400s for a tank that size. i have a 95 gallon reef with 2-175 watter and i'm considering going to 250 watters to provide extra light. hope this helps...

 

[luke]

You **CAN** have them as close as you like. The closer they are the less coverage you get side to side. I would recomend modifying the canopy to 12" (if possible) Then mount them so they are near the top of th canopy, giving you a good 8-10" of room. This will make working on the tank far easier, and will spread that light around. I agree that 2 MH is small for that size tank. I personaly feel you need at least 1 MH per 2' I like it even more often myself.
As for salt splash on the bulb: DON'T LET IT HAPPEN!!!!! People may report not having problems, but they can and do happen. These bulbs get VARY hot!!! When cool water hits them they are apt to explode. This does happen. If you have the bulbs close to the water, then cover the tank. The best thing that could come from this is a brken bulb... the worst thing that can happen is a burnt down house!! (I new someone that had something like that happen)
Luke

 

[biggdriver]

I don't know if this is try but someone also told me that salt can scratch the outler layer of the glass bulb when wiped off..Thus scratching the protective uv filtering lense on the bulb..anyone else heard of this.?In the long run I would be atleast 8-12 inches above the water and Also would go with 400w at about one every 2-3ft max..this also depends on what you want to keep in the tank ..Sps etc..

 

[gabbys125reef]

The closer you get the less coverage you have, and the light isn't dispersed evenly. Mine are 10" off of the water. You shouldn't get much closer than 6".
<a href="http://www.geocities.com/reeftank125" target="_blank">www.geocities.com/reeftank125</a>

 

[keitho]

well, as it turns out, most glasses and plastics are excellent UV filters (despite public misconception). i seriously doubt that there is a protective UV coating on the outside of the bulb. even if there is a film and you scratched it, i don't believe that it significantly reduces the ability of the film to filter out UV radiation. i wouldn't worry about it...i'm sure even corals in the wild see some amount of UV hope this helps...

 

[keitho]

well, as it turns out, most glasses and plastics are excellent UV filters (despite public misconception). i seriously doubt that there is a protective UV coating on the outside of the bulb. even if there is a film and you scratched it, i don't believe that it significantly reduces the ability of the film to filter out UV radiation. i wouldn't worry about it...i'm sure even corals in the wild see some amount of UV hope this helps...