lighting

I have an 11 gallon salt water aquarium. I'd like alot larger one, but I don't have the space.

I have 18W metal halides. The one that simulates morning & evening is 5500K. The daytime one is 7100K.

My question is how long should the morning & evening lights be on & what is the total time my aquarium should be lit in a 24 hour period to stimulate optimum coral growth ?

Thanks.

[Sndwave80]

There is not one good answer for this as it depends on when you are home (to look at it) and water quality. Your “morning” light, which is typically actinic, can stay on for your entire day cycle to create a good lighting spectrum for appearance and growth. So an example could be is the Actinic (or 5500K) will be on 7am- 7pm and your full spectrum (7100K) will be on 9am- 5pm. Now this is where your water quality comes in, the lower your water quality the greater your chances of growing excessive algae on your glass daily and now limiting your ability to view the tank you have work so hard to create. Another important factor to consider is generally MH only has a live of 8 months before they start shifting in their color spectrum and producing the “wrong” type of light for your system and coral growth. By limiting/ increasing the numbers of hours you are running the bulbs will also limit/ increase the growth of your corals/ algae. And in turn when you should think about replacing the lamps (bulbs). I change mine around every few months to simulate seasonal changes from 8-12hrs per day. Hope this helped a bit and there are several really good books you can find at your LFS (I tend to use Petco for my books as they go on sale a lot) which can break this down even further. Thanks!

[MDeth]

I wouldn't run either spectrum over my tank. Both are very yellow and will grow coral...but it wont be pretty.

Also, 18W is on the extremely low side. Where/how/what purpose are these light supposed to be for?

I have a reef tank so I am using them for growing coral.

[kedron]

what is better 10k, 15k, or 20k, mine are 10k and i like the shadow effect but what is better for my corals or does it matter

[geekdafied]

K=kelvin which is color temperature, spectrum is measured in nm=nanometers.

As for which K rating, its all up to whatever you wanna do. 6500K is the best for growing coral, but is not very aestitic. 10,000K is crisp white, 15,000K is blueish white, 20,000K is blue.