mysteriously dying fish and corals

Question
I have a 180 gallon tank with a 45 gallon sump.  The tank has been running without any problems for 3 years.  I have a reef concept protein skimmer, a dolphin pump running approx 6000 gph and two 400 watt metal halides. There is a about 200lbs live rock with a 3 inch sugar fine sand bed. For my water changes I use hard water(unfortunately) filtering with a RO unit to 80ppm and use Seachem Reef Salt.

I currently have a large regal tang, a med brown tang, a orange tail Gobi, a dragonette, a very large chocolate chip star, a brittle star, a coral banded shrimp and a raccoon butterfly taking care of a very minor apatasia problem.

For corals, I have pulsing zenia, several tree corals or the same orientation, several mushrooms polyps, a folded leather coral, a large candy cane coral, a hammer head coral and a bubble coral.

The salinity is kept at about 1.025, the PH at 8.1 dropping to 7.9 at night.  calcium is 400ppm, nitrates are about 10mg/l, temp in the heat wave is about 83 degrees F for about the past 3 weeks, normally sitting about 80.

So for the problem:  A couple nights ago I noticed that the water had a yellowish/greenish tinge to it so I added some fluvel carbon to the sump with cleared up the water the following morning and I took note that corals were extremely plump and looking very healthy. Then to my surprise the following morning they were shrunk up as if in distress.  I was not sure what the problem was so I observed for a day and the following morning there was no improvement and both the butterfly and brown tang were dead!  I checked the ammonia it was at .1mg/l so I did a 25 gallon water change which brought the ammonia down to about .025mg/l.  I observed then for another day and didn't feed that evening, I added more carbon and put a 55watt T5 to the sump with kept the PH more stable at 7.9 through the night.  The following morning the remaining fish and inverts seem to be struggling some what, but are still alive, but all the corals are still shrunk and both the bubble and hammer head are dying rapidly. I have now done another 20 gallon water change and removed the carbon for fear of bad carbon, as this is the only new thing that was added before the problem began.

I am stumped on what the cause could be and have done all that I can think of doing.  Please provide your advice ASAP before I lose anymore livestock.

Look forward to hearing from you, thanks in advance.

Chester


Answer
Hello Chester sorry to here of your problems. To be honest I am really not sure as to what is going on. I have had this happen to me some years ago, but was because of stupidity, my decided to polish the hood with furniture polish, and it contaminated the tank. Wiped the whole tank in 3 days. One other thing I am looking at your temp, for me that is high that 3 degree jump could be stressing, and also maybe helping some type of free swimming algae or bacteria to populate. i really some of this makes since, also please ask some of the others on the site, maybe they can help further, i really hate for people to go through what you are going through now.