A question about Kelvin ratings

Hello,

I'm in the process of building my first reef tank, and it looks like I found a great deal on a tank setup that includes an Odyssea all in one light fixture with a 175W metal halide and 2 65W PC bulbs. I'm buying this used off of craigslist and the guy who is selling it suggested that it's time to replace the MH bulb.

Soooo....I was cruising the web looking at replacement bulbs, it looks like aquatraders has 175W replacement bulbs in three flavors: 10,000K, 15,000K, and 20,000K. Marine depot also has a number of 175W MH bulbs, including 5500K, 6500K, 12,000K, and 14,000K

I understand that the 20K's are bluer and simulate sun shining through clouds (thanks for the sticky Geekdafied), and that the 10K is a more yellow light. But
I was wondering what the implications of these differences are. Are there certain corals that prefer one end of the temperature continuum over the other? Is it just a matter of aesthetics, i.e. I like my tank to look bluer etc. Is one K rating more favorable (or unfavorable) for algae growth? What are the benefits and trade offs here?

Thanks so much!;D

 

I use 14k and love the look they give. It really all depends on what you like to look at.

 

Corals tend to grow better and faster with bulbs associated with the higher end of the light spectrum. The zooxanthellae also benefits more from bluer light than light from the other end of the spectrum advocating more reds. The red end of the spectrum will also entice and spur nuisance microalgae growth more so which should be taken into consideration. Personally, I love the 14000k-20000k bulbs with my favorite being the 20000k!

 

Cool, thanks guys. I got the fixture last night, after some research- I think I'm going to replace all the bulbs and the MH ballast as well.

 

I have used 10,000K and 20,000K. The 10,000K made my tank look very yellow which I didn't like at ALL. I will never use it again. I adore the 20,000K but have also heard very good things about 14,000K (never seen that one in action though...that I know of).

 

i run a 14k bulb, well two to be exact, and couldnt wish it to be any other color! its the perfect mix of blue/white IMO. But then some like more blue or more white. Personal preference, and mine is the 14k

 

It all depends on what your are trying to reproduce. 6500k which is basically sunlight is best for light loving corals cause they are found in shallow water when ther sunlight penetrates the most, but it tends to turn the corals back to their natural colors of yellow/brown/green typically. The deeper the water, the bluer it gets.

You use a good 10,000K with supplemental actinics and get great growth. If you're not using actinics, then go with 14,000K-20,000K. For the most, it comes down to personal preference. We think we have a little part of the ocean in our tank when infact we have nothing anywhere close to it. Most of the corals we have, with some exceptions, come from 10-20 meters down where the water is really blue. So its basically whatever you want your tank to look like. I personally use 10,000Ks and actinics on grow out systems and 14,000Ks without actinics on other ones.

 

I have been doing a great deal of reading about this subject lately and from what I've read the 14K Phoenix bulb is a clear favorite. The reason behind this is that it gives what appears to be the blues of a 20K bulb but the lower spectrum that corals like. So both owner and corals are pleased.

 

with regards to light, corals grow with a specific PAR. the only way to make sure the corals are getting the correct amount of "light" is with a meter. K values change the corals pigments by means of fluorescent coloration. also, different types of ballasts with different types of k bulbs produce different results. the element of pleasing the eye is more of a concern to people than what it takes to establish the correct amount of light dependent upon the coral genus.

heres a site, to make things a little easier.
Advanced Aquarist's Online Magazine - Lateral Lines: Classification and Terminology For Reef Aquarium Lighting
look at table 2

 

I have used all three and I agree with you about the 10k, too yellowish. I also think the 20k is too blueish, this bulb is for someone who doesnt have actinics(IMO). The 14k IMO, is the right choice, at least for me. It has the perfect blend of white and blue colors. Having said this, every comp. makes there bulbs differently with aspects to the K-rating. I have seen 10k, 12k,14k,15k, and 20k. Some 14k look like 20k and so on. Find one that you like, and stick with it.