Tank Cover

[Delphinus]

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!