Not to fire the flames of controversy, BUT , I am now able to add some real measurements to this post

I have again fired up the old 175W AB bulb (I was not running it due to heat problems.) It is now located eleven inches above my 20H. The Lux meter I bought from Dez some time ago has a probe that allows me to read the irradiance at the bottom of my tank. To make a long story short, I get a reading of 15,000 Lux at the bottom of the 16" deep tank. I am unable to discern a difference between readings with the glass cover in place or not. :eek:
The point is that if I am to go by what John Tullock says in his book, that 10,000 Lux is enough for most organisms I need not worry about the glass cover. If I can get used to the color I don't have to replace the bulb either. Unfortunately I like the looks of the 2X65W PC"s much better. :rolleyes:

I almost forgot another measurement. I have a piece of M. digitata that is growing well in my 50. The polyps are fully extended, and the tips are pinkish. The location is under 2X96W PC's under a 1/4 inch glass cover, and 8.5 inches under the light. The meter reads 5000 Lux. :eek:
I am providing this information so that you may all draw your own conclusions. :mrgreen:

Bump

Anybody see this in their tanks?

There are so many issues that can cause bleaching.

As for the UV question, I would have to say that I think the issue is "too much UV too quickly" not so much "too much UV." Now I've never worked with double-ended bulbs in an unsheilded situation so let's ignore that case, presumably there's too much UV from THAT; but I doubt you can really get too much UV from any kind of bulb, VHO, PC, or MH. However, going from one lighting situation to another, in a quick transition, can cause problems. It's like if you go to Cancun or something, if you acclimate yourself slowly to the sun you'll eventually be able to stay out in it longer but if you just spend the first day outside all the time, without sunblock, you're gonna get a sunburn.

These are the sorts of questions I ask myself if I notice something "odd" or "off" with a coral in my tank: How long have I had these pieces? Have they been moved recently? What situation with lighting were they in before? Are they in any kind of flow "shadow" ? Are there any neighbouring corals that could be interacting with them? Have I checked all your levels, pH, temp, NO3, PO4, etc.? Do I have macroalgaes nearby? mushrooms, leathers or softies nearby? etc.

FWIW, HTH, etc., ... good luck!

Hey Tony,
I wouldn't call it bleaching, the colors have just faded. A prime example is a frag of that purple Acro I got from you. When I got it the tips were purple, and the lower branch was green. Now the whole thing is a light green. I also have another acro that I have had for a long time that started out a light green, and is now a whitish green. I also got a frag from Evan at the last frag swap that was a maroon/purple color, it is now a light purple with intensely purple tips. Just trying to figure out if my tank was getting too much UV or not enough. Most of the corals have great color, just those 3.

Mike

Mitch mentioned to me that more flow might help in that situation. There was a lengthy article on Reef.org regarding the topic. He might be able to comment more or post a link to the article.

Dave

Shirley...

:smile:

http://www.advancedaquarist.com/issu...2004/media.htm

Mitch

Mike get some MH's for a wedding gift and those suckers will be super corolfull. ( Bob, that's not missplelled just a new word)

Dave

Question for Bob....

Bob, if you're using a cover and going skimmerless, how are you ensuring sufficient gas exchange?

Mitch

As for fading corals, I wouldn't keep acro's or any other "high energy reef zone" corals under anything other than MH. Those guys need high intensity light and high volume water flow.

Mitch

(jmho)

Covers don't fit tight. There are good sized gaps. My livestock appears happy :rolleyes: , so I am too. :mrgreen: