What is the optimal distance for metal halides from water

[ian]

I am having a custom canopy built for my 215 gallon reef tank. I have a metal halide lighting fixture that will be placed inside with 3 bulbs. Can anyone advise what the optimal distance from the water would be for the lights? I was thinking about having the canopy made either 12" or 18" tall.

 

[snakeblitz33]

Generally anywhere from 8" to 12". The main reason for the distance is so that you can put some very good ventilation in the canopy - by using fans, mostly. Your halide unit will also have built in fans if it is any good. air circulation is key. If you put the distance lower than 8" from the bulb to the water, you risk sunburning your corals. I would personally go 10" to 12" from the bulb to the water line.

 

[ian]

Awesome feedback thanks. I have been looking at some pictures over the last half hour and it appears a lot of people have left the back of their custom canopy open. Seems like a good way to keep hot air out.
One other question. Any thoughts on going without the glass top? I am worried it will cause damage to a wooden canopy over time but it sounds like quite a few people have done it.

 

[snakeblitz33]

glass top on a canopy? Never heard of that...

but if you are referring to the glass top on top of an aquarium - I would definitely remove that. It prevents gas exchange which lowers your pH. If you are going to put a top on your aquarium, I would use egg crate - since you have such a long tank, I suggest cutting it into two foot sections. Or is your tank only 6ft?.... eh, 2 foot sections would still work.
The top of the canopy can also be completely left open on top. You can mount the fixture in the stand creatively and make a lip all the way around the top of the canopy and put an egg crate top on it. This really helps gas exchange, and ventilation. Especially because heat rises.
I make custom aquarium furniture.... so I know a thing or two about it.

 

[ian]

My mistake but you figured it out, glass top on the aquarium is what I meant. What would be the benefit of egg crate? Is it to keep some of the moisture out of the canopy? Better question with your level of experience is, have you seen damage to a wooden canopy without some sort of barrier?

 

[snakeblitz33]

The benefit of egg crate is to keep expensive fish from going carpet surfing and ending up as french fries on your floor.
Moisture... unfortunately... will happen.
When I mentioned making the top of the canopy with some egg crate - it's for the ventilation. If you can keep it well ventilated - because heat rises - then there won't be as much moisture build up. If the top of the canopy is enclosed, the heat has nowhere to rise but out the back of the canopy, close to the wall - which will heat up your water more than you wish.
Also, I hope you are aware that you should either paint the inside of the canopy a light color such as white - with a high gloss primer and paint to keep moisture from seeping into the wood. OR, you can stain the inside of the canopy and apply a good coat of polyurethane on it. There yah go - two different methods to prevent water damage.