Metal Halides - 400w vs. 250w

[captexas]

I am still working on how I want to do my lighting on my 240g reef tank. I currently run 400watt halides on my 75g. I have never had anything else other than the 400watters so I'm curious to see how people that have had both 250 and 400watt halides would compare them. Obviously 400watts will give a lot more light, but I want to know how it affects the corals. I've been debating on going with 4 or 5 metal halides on the tank, whether to go with 400 or 250watt lamps or maybe a mix (250-400-250-400-250 or the other way around 400-250-400-250-400). I wouldn't mind stepping down to all 250s on the new tank to save some on electricity and get a little softer lighting as long as the corals and clams will still do well. My two 400watt 10k XMs are very intense on my 75g tank and I have had excellent coral growth.

[dan]

on my tank now i'm running 2-250 10k and 1-400 20k. i really like the mix. i'm also running 4- 4' VHO 2-white and 2-blue. on the tank that i am now setting up i will have 3-400 and 2- 72'' VHO blue and hope thats enough. tank is 84''long x 36'' wide x 26'' tall. 340 gal.

[Instar]

All the watts to consider is really not the only consideration. The distance they are from the surface or the interval will also play a large roll on the amount of all those watts that gets into the tank and to the coral. If you have to keep the 400 watters way up high to prevent heat issues, then they may not even be as effective as a 250 mounted closer to the water with a good mirror reflector. So long as you have the mix right on the wave length and enough total watts getting into the water, the clams and coral will do great under 250's with VHO's.