what would cause some of my coral to completely bleach in a day?

what type of lighting are you running

 

Everything was fine until the last couple of days?
Have you dosed anything?  What changes have you made (if any)?  Have you released anything into the air around the tank?  Cleaners/bug spray/etc?
Possibly contaminated the tank with something on your hands when you put them in the tank?
Skimmer going crazy is usually (not always) an indication of something in the water.
Could something have died that you're not aware of?
What's your ammonia/nitrites/nitrates?
Got pics of the bleaching?
-Eric

 

Are you monitoring the amount of strontium/melo and iodine in the tank?  BTW - what's melo?
I'm not a big fan of dosing - especially without testing!
-Eric

 

Just curious but were these your first sps or have you been keeping them? I'd also give your bulbs a good looking over, check for cracks etc. It seems odd that whatever it is would be bothering such an array of different typed corals. How old are your test kits? It would be good if you found a local reef keeper and cross checked your results on a different set of test kits. To me it sounds like high nitrates but thats only my gut. If your close I have plenty of kits and could probably come take a look if needed.

 

Are you sure that the corals are bleached or have they lost tissue? Typically tissue loss occurs very fast compaired to bleaching in sps corals.

 

Melo? Or Molybdenum? I wouldn't dose any of those trace elements or Iodine. Too easy to screw up the balance. The best way to replenish these is with bi-monthly or weekly 10% water changes.

 

Yes Chris I would also wonder why you are dosing those elements? You should never dose what you are not measuring, I am guessing you are not measuring those three. Iodine overdose can be very bad as I understand it, I don't know about the other two but have never dosed them either. IMO opinion those fancy bottles of trace elements are there to steal your money, good salt and good water changes will take care of them like mentioned. Other than the normal pH, salinity, temp, NO2, NO3, PO4, Ammonia and the such pay close attention to CA and Alk. What are these numbers? Low Alk can cause problems with SPS for sure. I would leave it to others up here to say whether low Alk would cause the problem with the slimer and tort but my opinion is yes. The softies probabally not.
I don't remember what bulbs you have? I am thinking they are new though right? Not Ebay bulbs? Like Jason said old or Junk bulbs is another very good possibility.
This is a new tank so I am thinking water params, could be contamination like Eric has mentioned but since this is a new tank I lean towards the more obvious of water and light. Lets concentrate on water quality and lights and get these saved. You should maybe get carbon running in case there is a contamination heavy metals or something. You can call me if you want.
OH and you are using RO/DI right, I forget.

 

Alk over 4 can also cause SPS to bleach. You need to try to keep it in the 3-4 sweet spot

 

Again...are they bleached or have they lost the tissue? An alk of 4 meq/l is not likely to cause bleaching .....that's about what IO and reef crystals mixes at

 

Sounds to me like typical tissue necrosis on the sps. Although many times there is no real indicator as to why a piece sloughs tissue, I'd say since the 2 pieces you have are generations old in captivity it is your water quality compaired to what they were in. Your best bet is to cut any living part well above the loss line and take out the dead/dying part as it will only pollute your water causing more stress.