Metal Halide Q&A

The radiums are just more popular because they are SE and most fixtures come in SE.

72" is a hard length because you can do two or three. Since you probably don't mind the electricity then go with three. With two you can cover most of the space and have the t5/vho offset to take up the slack for any spots in between and on the edges.

Galaxy makes good ballasts... But also check out lumatek. I think it's the same company just different brand but the lumatek has selectable watt ballasts

 

Would 3 250s do me better? I don't really plan to have any livestock in the front 6" or back 6" and if I do it's going to be LPS anyhow.

 

With the big reflectors it's hard for a 250 to get the spread and the depth. It could work though. If you get the lumatek 250/400w select-a-watt ballasts you can decide which works for you without buying a bunch of ballasts.

 

It all depends on if you want a noticeable hot spot. This combo will get you what I think would be the best overall spread without an obvious hot spot. The reflectors are nearly 23" x 23" so a third will not fit. Even choosing 3 smaller reflectors you would have a lot of wasted light due to spill-over on the edges. The Lumenmax excels best at 36" x 36" light spreads.
here is the link to the reflector
LumenMax Reflector for Mogul Bulbs - Sunlight Supply - Bulk Reef Supply
Below is a friends tank who I had the same conversation with. He replaced his previous lighting of 3 400w spider reflectors across the front with 2 175 watt with spider reflectors across the back. He was blown away at how 2 premium reflectors could replace and outperform his 5 metal halide configuration. Here are pics of his tank to see how the coverage is.

 

The 300DD is a 72x36x27 tank has 2 braces I hate to mount a point source light directly over a brace. Should I just not worry about it?

 

How wide are the braces?

 

I think it's about 3 inches.. Assuming it's the same width as my marineland 210tall

 

Steve made a VERY good catch that I missed out on here!!! (thanks steve)
Most DE bulbs must be UV shielded with a piece of glass. The SE bulbs have enough shielding in the bulb glass themselves that it is not essential to shield, but the DE are thinner and more low wavelength light can pass through... sometimes being in the harmful UV spectrum.

 

If that thin I don't see it as a problem as the a lot of the light is coming off the reflector which is what makes this reflector have such and even distribution.

 

It will be a noticeable shadow from the brace if its placed directly above it.
The t5 will help to disguise it but you will still be loosing a good bit of your most intense spot.

Have you thought about using a light mover or two? its really a personal preference but I am using a mover with a lumenark reflector over my 4x2x2' 120g. You can PM if you want more info on movers.