Sounds like a bacterial bloom.
So if we dont know the cause, I would suspect a dead creature somewhere in your tank/rock.
But, in the meantime, add extra oxygenation to prevent bacteria from using up the oxygen and killing everything in your tank. Skim wet to help remove the bacteria. Doing a partial water change can help, but in all likelihood the bacteria will just repopulate and make it cloudy again. Keep some freshly mixed saltwater to replace the skimmate. Empty frequently.
Personally I wouldn't do much more than that, unless you start seeing coral go downhill. If you do then do water changes, maybe every other day.
Edit: whoa nitrate 80... missed that. Yeah giant water changes every day for a while if that number is right. How old is this tank? Did it get cycled properly?