Corals and fish mysteriously dying

Question
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: thats not good, well you did exactly what i would have done in adding carbon. do any of the fish look like they are breathing heavy? the green tinge sounds like an algae bloom and could have sapped up O2 in the water, having done that it would have caused a PH crash as C02 rose in the water.

may sound odd but check your water for copper, perhaps could be contaminated carbon?

do you have anything metal near or around your tank? my mate had a wire mest over a hole he cut in his hood to allow light from hi hallide through, it rusted a bit and contaminated his whole tank.

give me a shout back i will have a chat with some mates and see if we can't perhaps come up with something.

good luch and i hope everything is ok

---------- FOLLOW-UP ----------

QUESTION: Thanks for your prompt reply.  In response I don't think that there was an algae bloom,Due to my tangs being lazy i have quite a bit of hair algae I do have quite a bit of green hair algae growing on the back glass, I keep the front and sides pretty clean and my tangs seem to be too well fed to feed what is readily available. i haven't been concerned about what is there really as it seems to keep my phosphate levels down. As for the suggestion of low O2 in the water, I am doubtful of that also as my skimmer is pumping alot of O2 into the water as well as the water crashes into the sump which would create agitation. The other fish seem to holding their own, but barely, I did notice that yesterday the regal tang seemed to agitated, flighting around the tank and breathing heavily, but today he is eating the flake I have added.  Yesterday the dragnet seemed to be unbothered and now today he seems to suffer from shortness of breath??  The Candycane Coral seems to have been unaffected with the whole thing, while the tree coral and zenia and mushrooms are completely shrivled up and the banded coral and brittle have survived...Very puzzling.  I have now removed the bubble coral and and the hammer head and put them into a reserve tank to watch their progress, but positive the hammer head will not make it and the bubble's fate is left to be determined.  Upon your suggestion I have rechecked the copper levels, which came back with a 0 reading or as close as we can tell with the color chart provided.  I have also double checked for any metal which may have hit the tank, but have not found that to be the problem. The carbon has been removed and now replaced with a couple bags of Chemi-pure hoping for some improvements with that.  In addition to all of this, after standing back and looking at the tank, it seems to be very colorless and dull, the algae which is usually very full and vibrant green, seems to be looking dull and almost brownish, everything just seems to be overridden with death.  

I really appreciate your help and any that your friends can provide.

Thanks again in advance and looking forward to hearing from you.

Chester
ANSWER: really is a strange 1, just as a quick thought see if you can get hold of some polywool, it changes colour indicating if the tank has been contaminated.

i don't suppose you have disturbed your substrate under your rock work or recently moved your rockwork? if so its possible that hydrogen sulphate could have been released into your water from the compact and detritus rich substrate under the rocks. (kinda grabbing at straws here as it has me a little stumped and i havent had the chance to talk to my mates yet) also ask the other experts on here, they may also be able to shed some light on it

---------- FOLLOW-UP ----------

QUESTION: Sorry to give you a headache with this, it is bad enough that I have one along with some heartache.  As I am sure you can relate it is very disappointing when something like this happens.  Thanks for the tip with the polywool, something I didn't know.  I am going to give it a whirl and see if it comes up with anything.  You know I have been running a tank for 9 years and there is always something new to learn.  I will keep looking into things and if you can come up with any further suggestions they will be accepted willingly.

Thanks again

Chester

Answer
yeah i can relate, its a great hobby and when something like this happens its almost like your back at square 1.

i have only been keeping marine fish for roughly 18 months so i am quite your junior!! i guess i have been very lucky and have had relatively trouble free reef keeping (touch wood)

if your not already signed up, try www.ultimatereef.com its a forum with a few thousand members and i am sure collectively they will come up with something for you, they were the guys i was gonna ask in the first place.
also try www.tropicalfishcenter.co.uk its a smaller marine community but there are some really clever guys there who really know their stuff.