Hello, guys,

I've got a 220gallon reef aquarium that was put up several months ago (almost everything in it came out of a 75g tank that had been established for over a year before we switched to the bigger tank). I've never had any issues with the coral, bubbletips, and inverts, and most of our fish have been doing phenomenal (the only fish we've ever had issues in not keeping is the mimic tang that for some reason we just don't have luck with). There's absolutely NO aggression in this tank. Everybody swims around and acts happy and eats a varied diet. Currently we have: Vlamingi (still young about 5in), hippo (still young around 4in), melanarus wrasse, cleaner wrasse, flame angel, two snowflake oscellaris, mandarinfish, 4 firefish, yellow watchman, diamond goby, sleeper goby, starry blenny, foxface, and 4 green chromis. We've also had a 3.5" Carpenter Wrasse that has been very healthy up until now. Swimming, eating, no signs of illness whatsoever (I've been an aquarist for 14 years and know when a fish is acting or looking odd). Literally, 30mins after seeing him last, he's floating around the tank covered in mucus (I assume the mucus he cocoons in for bed). Is it possible he could have suffocated in this? Params been stable and where they need to be.
Nitrates/Nitrites/Ammonia: 0
PH: 8.0
Temp: 77F
Salinity: 1.024

Anyone have any ideas? Much would be appreciated!