so I know that sunlight is like 5500-6700k and i think we use 10k bulbs to help avoid algee growth, but what about 8k? would a light fixture with 8k, 18k, 8k, 03 actinic cause algee issues? would this be good for coral growth?
I would have to go with what has been proven. Not saying these bulbs wouldnt work just that I couldnt spend my money on them till they had been proven. Also the only thing that leads me to believe that they may not be successful is that its kind of like ,,,, when your suppose to cook something at 350 degrees for 30mins and you say ahhhh I'll cook it on 700 degrees for 15 mins. Lets guess how that turns out. lol
The lower K spectrum doesn't necessarily cause algae issues. The old Iwasai 6500 K metal halide bulbs were very popular years ago when they were one of the only choices and they will grow corals faster than most higher rated Kelvin bulbs. The issue that comes into play is coral coloration and coloration as it appears to the reefkeepers eye. The Iwasakis will color corals up nicely (albeit different from say a Radium 20 K bulb) but a tank lit by lower kelvin bulbs, especially with no atinics, is too yellow to be appealing to most.
Here is a site with pictures comparing the look of different kelvin bulbs with and without atinics(click on 250 watt metal halide testing on the right under links): http://www.cnidarianreef.com
Of course I am discussing metal halides and it looks like you are considering flourescents from your description. Hopefully that will clarify a little of what you are asking though. Another thing to keep in mind is lighting manufacturer's listed K ratings are more for marketing than what they actually are so looking at a chart of the specific spectrum will give you a better idea of what a bulbs output is.