Help with Bleaching???? Please!

[Mich3417]

I have a 150 gallon tank with a 25 gallon sump ( I have a Monaco method set up). The tank measures 5ft in length, 2 ft wide and about 2 ft from top to bottom of the sand ( I have a 6 inch sand bed). The tank has been up for about 1 year. I have placed a lot of frags SPS, LPS along with some soft corals, colt,mushroom, polyps ricordia... My water parameters are all good, except I let my salinity dropped below 1.020 for awhile, a little over a month ago (careless and lazy). My xenias were the first to die; they just melted. I corrected the salinity and noticed about 2 weeks later some of my acropora were bleaching. I really do not think I can contributed this to the salinity since it has been corrected now more then a month. The only thing I can come up with is could my tank being getting too much light? Four completly blue actinic VHO (110 watts a piece go on at 7:00am-9:00pm, followed by two 175 MH that turn on 8:00am-8:00pm and finally two 275 MH from 9:00am to 7:00pm. The lights are aproximately 20 inches above the corals which are bleaching. They are not shielded by any plastic or glass. My question is, could my corals be getting to my light or two much UV radiation? I have been a reefer for about 10 years but with mostly soft corals and VHO lights. This is my first time (this past year) with hard corals and this bleaching is driving me crazy...I would appreciate any advice!

Thanks for your help! Mike

[reef_noob]

Hmm, could be that they are reacting adversely to toxins from the softies, or that the salinity is pretty low. Of course, there could be any number of other possibilities.
I think it unlikely that they are getting too much light, unless they are recent additions and you didn't acclimate them to the light properly.

If you post what you are testing for, and the test results, some of the reefers who are more knowledgeable than I may be able to suggest some other possibilities.

[tims]

Afternoon mike,
the bleaching maybe coming from the lighting , what is the temp. of the tank withh the lights on? measure directly where the bleaching is. there are several scientific papers the suggest the symbotic bacteria are dying off and changing. excess heat is what they are suggesting.
the low level of salt most likly helped this along.
you really need to be running carbon all the time if you have such a large mixed of corals too. the chemicla warfare between them all may also kill off a few.

[wharyat]

I second the chemical warfare; unless you just recently added or replaced those MH.