Green monti cap melting

Can you get a second picture of it?

(might raise hell) but 83 isn't warm, 90+ is worrisome if sustained, but I keep my tanks at 84. The temp ranges we keep now are still carry overs form a time when DOCs were running rampant in our tanks and there was little O2 exchange from the tank surface because of protein build up from the lack of skimmers. Lets all evolve with the hobby as well!

Rant aside, rapid necrosis is a sign of potential problems. You will want to remove or isolate the coral before it sets off a chained spike in the tank. Other than that if you are using a reputable test kit ( other than API) you will should see if there is an evident issue. Because you haven't seen anything yet I would point my nose toward something picking at the coral, lighting or placement.

You can try and save what you can by cutting the living parts off the coral from a few cm away from the necrotic line. But this is not guaranteed to help just a shot. If the area that is cut begins to rot as well then it's trouble. Either way its either a bacterial infection or die off caused by intrusion and water quality...

 

What is your tank temp normally? . If you normally run 78, then 83 is a huge swing. Try to get your temp stable as you can before it spreads

 

I assume the light is trained on it to show the coral and its mot normally spotlighted on it right?

 

STN and I think Craig is correct- the temperature creep. Have you changed salt lately and/or had other param swings in the past year? Such as dialing in the CA reactor, nutrient issue, etc?

FWIW, SPS's need the most stable environment possible. People think that they are "home-free" when they don't see issues right away from having instability. This is a false perception. RTN, STN and tank crashes can occur 6 months or later after a tank has gone through instability of almost any nature.

If you are seeing a slime/jelly like appearance on the cap, I would remove it asap! That sloughing could cause more problems being waterborne. Good Luck! :0)

 

dont suppose another coral could of stung it eh?

 

I had a temp spike a while back and only a few sps colonies were affected. The corals right next to them were perfectly fine. But mine was slow recession so I was able to cut and save all the peices. Make sure your alkalinity stays stable or more corals may start also. Good Luck.