Lighting wattage - how much is too much?

[Funky_Fish14]

I have a 75g with 2x 400W Metal Halides, both a 20K and a 10K, and all the corals are doing fine and love the light.

Chris

[Delphinus]

(Moving into the main reefing forum...)

IMO, it's more a question of acclimating corals to that intensity, instead of what the overall intensity actually is. If a coral is moved from a less intensely lit environment it should be acclimated gently (using an on/off light method .. e.g., start off with 1/2 hour on, 1/2 hour off, for a few days, then 45 minutes on, 15 minutes off, and so on).

There will be some things though that don't really appreciate super intense lighting, mind you, so species selection will have a role (although as Harvey says, you can get away with putting some of the ones over at the edges).

Fish and anemones, no real concern. Softeys, probably not so much. LPS yes, need to be careful. SPS and clams .... will looooooooove those lights.

[StirCrazy]

ok one thing no one has asked is how tall is the tank, if it is 24" then 400's will be fine, if it is 18" then ya you can use them but I would be carefull getting things used to the light.

Steve

[Psyire]

Something else that should be mentioned too...

If you use a 14k or 20k bulb, the PAR will be lower and you can go without the VHO's. 14/20K bulbs in the 400w range have a PAR similar to 250w bulbs in the 10K range.

10K = White
14K = White/Blue
20K = Blue

(The aboves are the norm, but ofcourse they vary with company)

[Ruth]

The other thing that will make a difference is how far you have the lights from the top of the water. The higher you have them the less intense the light getting to the lower part of the tank.
The other thing you are going to have to watch is heat - those lights generate a lot of heat and can overheat your tank. It may not effect it too much right now but in the summer it could be an issue.