View Full Version : MH Distance

04/09/2007, 09:37 AM
I have had a 75g SPS tank for about a year now and my corals have always lacked a little in color. Well, over the last few months most of them have started to grow towards the top of the water and now all of the sudden the tips are starting show tons of color. My MH's (250w XM 10K) are mounted about 14 inches above the water, so I was wondering how high everyone else's MH's are mounted over their tank?

I'm starting to think mine have just been mounted to high all this time... :(

04/09/2007, 10:10 AM
Maybe, most keep around 10"

04/09/2007, 10:18 AM
8" here.

04/09/2007, 10:21 AM
Reflector plays a big role along with what amount of area you are trying to cover.

04/09/2007, 10:21 AM
7 inches

i say as close as you can get them without overheating the tank and still gettting the spread you need.

04/09/2007, 11:26 AM
14" seems a bit too high.. i keep mine between 5-9" depending.. just make sure you don't have tank temp too hot or splashing onto lights..

04/09/2007, 11:44 AM
I'm using the spider reflectors and have electronic Coralvue Ballasts running the XM's. The tank is a standard 75g that's 18 inches high, so I didn't think the height would matter but the color is just so much better at the top of the tank.

In the MH article this month the author stated that he setup his test unit 8 inch's below the bulb because that was a common distance.

I finally settled on a 2' x 2' x 2' square box (seen above). Its inside was painted flat black to minimize the amount of light reflected back to the sensor. The mogul socket was mounted horizontally, approximately 5" from the ceiling of the box. The quantum sensor (a sensor used to measure PAR) was placed 8" below the center of the arc tube. I chose 8" because this seemed to be a common distance that people keep their MH lamps from the water's surface. To minimize voltage spikes and aberrations, a voltage regulator was used on power from the wall's electrical socket. A watt meter was plugged into the voltage regulator and the ballast plugged into the watt meter.

And the PAR level for my exact same setup should be:
CoralVue Electronic Ballast:
Lamp (XM10K) - PAR (541) - Watts (257w)

So if add 6 inches to that the PAR would be significantly less correct?

04/09/2007, 11:54 AM
I have mine 6.5 inches above the water surface.

04/09/2007, 03:46 PM
i have a 75gal with 2x150mh 2x96, 10" above water and i'm afraid to put anything on the sand.

my 120gal 2x400mh is about 8" above water, and i think 8" is perfect.

04/09/2007, 04:10 PM
about 8" i felt that was the best height to set them at seemed like best coverage and intensity