Sounds to me that the coral may have gotten stressed out from 4 things:

 

1) Temp rise to 83 degrees is pretty much the maximum acceptable level. Corals can start to bleach, or even die off at 84 degrees.

 

2) Warmer water also holds less oxygen than cooler water. Combine that temp rise with your turning down the skimmer, and the available oxygen level in the water may have dropped considerably.

 

3) New light bulbs = change in light intensity and spectrum. Corals can be sensitive to changes in lighting.

 

4) Possible chemical influences from other corals - especially soft corals.

 

 

As far as dealing with the Brown Jelly:

 

1) If a single head shows up with this disease, remove that head and any nearby heads immediately - even if the nearby heads look OK. Brown Jelly is a highly infectious bacterial disease. Perform an iodine dip on the remaining coral.

 

2) If more than 1/4 of the total coral is infected, throw the whole thing out.

 

3) Change your carbon out for fresh carbon, but do not do a water change unless you have some other issue (like high nitrates) that needs attention.

 

4) Keep a close eye on the rest of your LPS corals to see if the infection has spread.

 

 

Good Luck.

 

 

 

also, are there any other corals upstream from it? Some chem warfare from another coral stressed by a temp change may be the cause. In this case, change your flow and add some carbon.