Lights on for how long ?

[FitoPharmer]

too much light depends on what your keeping and your tank. Too much light usually means too much heat, that will kill corals. But corals can also be killed from just too much light (bleaching by either intensity or duration) the symbiotic algae inside the coral can no longer take the conditions. If your corals are looking good, growing, and color is usually a good sign, your light is not too strong or on too long. Given enough time and the right conditions, it is crazy how much corals can adapt to light changes.

[Parker]

Originally Posted by FitoPharmer

too much light depends on what your keeping and your tank. Too much light usually means too much heat, that will kill corals. But corals can also be killed from just too much light (bleaching by either intensity or duration) the symbiotic algae inside the coral can no longer take the conditions. If your corals are looking good, growing, and color is usually a good sign, your light is not too strong or on too long. Given enough time and the right conditions, it is crazy how much corals can adapt to light changes.

Very true, I was speaking more to the point that people are saying corals stop up taking light without negative affects, IE: 8 hours of light vs. 5 hours of light. The corals are not affected by being lit for 8 hours but after 5 they are no longer benefiting from it. This all assuming optimal conditions such the 8 hours of lighting isn't over heating the tank etc.

Again, I have no idea how much truth there is to the theory outside of the extremes, I was simply speaking to what I have read. It might be a pile of crap for all I know.

[BC564]

I run my lights for 6 hours a day....3pm - 9pm

[DiverDude]

ok...well I don't have any corals right now but I'm thinking of adding them in the future (hence the research on metal halides). Reading between the lines though, the general consensus is that ~15hrs a day my PC lighting is running now is not likely harming anything but it is probably wasteful.

OTOH, if I had MH, then 15hrs might, in fact, be bad.

[DiverDude]

Did more research and was having a lot of trouble finding 75W metal Halides (I have a centre brace in my 29 Gal tank and don't want a shadow from the brace so 2 lower wattage lights would be needed instead of a single lamp) and came across a section of the USHIO website that was quite informative:

http://www.ushio.com/products/petcare/aqualite.htm

In it, they state that MH lights should be on for at least 12 hrs a day...

No telling if that's a marketing ploy to use more lamps or if that's from a sound biological rational.