20k bulb better for corals?

[runway1]

My lfs tells me that 20k bulbs are healthier for corals. Opinions?

[electrikat]

I don't know about healthier but they are definitely prettier under 20k. You also don't need to supplement with blue actinics when you use either 14k or 20k bulbs. This saves on electricity and bulbs. They also make the whole tank sparkle and beautiful.

[captivereefs]

Most sps do seem to color up more under them but that is when they are overdriven with an HQI ballast. The bulb will have a shortened lifespan when overdriven though and should be replaced a 6 months. I still think the 10K is the best all around bulb and the 14K if you do not have actinics. All tanks are different though so you can always experiment which is part of the fun in this hobby!

[CBRGuy]

that best PAR value for coral is 6500K, which means that you will get the most growth, but the coral will look yellow. 10k will give you growth, and good color alone with good growth. 20k will give you better color but less growth.

[runway1]

I never can trust the info at the lfs. It's almost like....ask and then do the opposite. I was told that the 20k helps the corals "process" their nutrients and grow better.

Of course, I was also told that anything more than NO lights will require a chiller!

[CBRGuy]

Here is a test from Sanjay. This test doesn't show the 6500K results, but is does have the 10k and 20k. There is also another test, which show pictures of the corals under the different lights.

http://www.advancedaquarist.com/issu...5/feature.html

[captivereefs]

Do not just go with PAR alone. There is other factors as well like CRI and lumen output and actual light absorbsion by the corals. How corals actually use the light is stil not fully understood so every tank set up wille different then the next. The best bet is experiment over time and share the results!