How high????

Captain Nemo · Mar 24, 2011

So this kind of a dumb question, but to maintain the best PAR levels and all, how high above the water should my 250w MH be?? It is roughly 20 in from the sandbed to the light right where it is now. If I move it up, I get more coverage, but am afraid of losing PAR, I appreciate all your thoughts...... :nerd:

Captain Nemo · Mar 24, 2011

bump for help.....

chris goetz · Mar 24, 2011

That will be very tough to answer without knowing the specifics(ballast, reflector, bulb, corals, etc...).

FWIW-I run 2 250w radiums in LumenMax Elite reflectors(with glass shield) on Lumatek adjustable ballasts at the 250HQI setting about 15" over my 24" tall 120 and I measured 100-150 par in the corners on the sand. I was getting 900 par 1" below the water directly under the bulbs.

To clarify my bulbs are 15" from center of bulb to surface of water.

Captain Nemo · Mar 24, 2011

Thanks! To clarify, I am unsure of the make and all of the light and ballast, but know it is a 250w. It is a one piece housing with actinic in the housing with the halide and glass shield in place. It is a 20k Reefbrite bulb brand new one at that. Does that help?

Captain Nemo · Mar 24, 2011

bump.

butts182 · Mar 24, 2011

It also depends on what corals you are keeping in the tank. It's not an easy question to answer, but at only 20" from the light to the sand, I would say that you could increase that by 1 foot and still have pretty good par numbers. the tank must be shallow.

Captain Nemo · Mar 24, 2011

No the light is only 5-8 in off the water. It is a deep tank.

Wy Renegade · Mar 24, 2011

Distance the light is above the water is relatively null and void, as air does not affect par. Depth of tank is significant as depth affects par, however you will get roughly the same par at the top of your tank if the light is 12 inches above the water or if it is 5 inches above the water. However if you have a very deep tank, par will change at the bottom because the light is closer or further away, if that makes sense. In my 65gal with 250w MH, I kept the light about 10" off the water's surface, mainly because that gave me enough room to be able to reach into the tank without having to remove the light (although it was close enough that I burned myself a couple times on the light). I had sufficient light at the bottom to grow any coral I wanted. My buddy with a 210 and 150w MH keeps his lights about 12" above the water, and is able to keep SPS throughout the tank. If it were me, I would go for about 12" off the waters surface.

Captain Nemo · Mar 24, 2011

Thank you for the very informative and excellent anwser! That is what i was looking for!

EliteReefs · Mar 24, 2011

that would make your tank only 15-12 inches deep so it is not deep at all.

you would bring you bulbs up to aroun 10-15 inches off the surface of the water easy and still get nice numbers. keep in mind this is a GENERAL statment. ballast type, and reflector play a HUGE roll in how true what i just said is.

Captain Nemo · Mar 24, 2011

ok, so to clarify very specificilly, water is 18-20 in. deep. light is suspended above the tank. 5-6 inches from the water level( top of the water), Shoudl/Can I raise it more and keep the same PAR??