20k - 10k MH's

[Chris Lakies]

What do you think?

I just purchased 2 175 watt Ushio 10k which will be replacing my current 20k Coralifes.

(A) What should I reduce my photo period by:

1. 1/4
2. 1/2
3. 3/4
4. no change

(B) What period of time should the light period be increased:

1. Couple days
2. 1 week
3. 2 weeks
4. More than two weeks

****I was thinking of decreasing the photo period by 1/4 and then increasing by one hour every day until I am back to the original length****

Back ground:
I am running my MH off of Blueline E-ballasts. I also have 3 110 watt VHO's, one Actinic White and two Super Actinics.

My tank is 55 gallon with quite a few SPS frags and softies. My newest addition is a nice sized Brain Coral (Faviidae)!

My light hood is not adjustable as far as height goes. All of the lights are approx. 3 inches off the water with glass tops between the water and bulbs.

[zhenya]

Hi Chris, what's the wattage of the bulbs that you're replacing?If they're same 175's I wouldn't change a thing. I actualy replaced 175w with 250w and only rased my hood about 2" for a whole wopping three days and did not see any problems with corals or clams.

[Reefland]

(A) - 3.
(B) - 2.

I do not know the difference in PPFD in these two bulbs but it surely wouldn't hurt to decrease the photoperiod and bit and ramp it back up to your normal day over the course of a week or so.

Just my thoughts, it's hard to be overly cautious.
Scott Z.

[Ninong]

Chris,

You're on the right track to be concerned about the difference in intensity between these two different 175 watt metal halide lamps. There is no question but that the 175w 10,000K Ushio is much stronger than the 175w 20,000K Coralife.

I don't remember seeing any test results on the Coralife but here is a link to test results on the 175w 10,000K Ushio and the 175w 5500K Venture: http://www.personal.psu.edu/faculty/...omparison.html As you can see, the Ushio puts out 63.41 PPFD compared to only 20.10 PPFD for the Venture when both are run on the same magnetic ballast and measured the same 18" from the sensor and both are run without reflectors.

In natural coral reef conditions it usually takes a coral about three weeks to adapt to drastic changes in lighting conditions. There are a lot of changes physiologically involving their zooxanthellae that have to take place.

A conservative recommendation would be to reduce the metal halide photoperiod by 50% and gradually ramp up over a 3 - 4 week period. I wouldn't make any changes to the photoperiod of the fluorescents.

[Chris Lakies]

I just recieved my Ushio's today and put them in. Wow they look great and much brighter than the 20K Coralifes!

I decided to go from 10 hours of light to 3 hours and ramp up 1 hour every day till I get back to 10.