^^These are very hardy fish; they could have lived through something which might have wiped out all the others. I'm still leaning towards disease, since (I believe) you said your corals/inverts seem unaffected.
I have some fish that were never affected by velvet but I qt them anyway because it will put it back in the tank. You may need to watch I don't think this I's a 02 thang at all sounds like a disease. You just have to think about it like I did good time to add corals lol.
Sorry to hear about your loss, if it helps this happened to me about 2 years ago in my 2 year established mix reef nano tank. One day came home and the 1 year + clown fish, bicolor goby, 6line, Cleaner shrimp,and mandarin were all dead. Only thing that lived was the larger of the 2 clownfish....and he looked 100%. All 50+ pieces of coral fine, EVERYTHING and i mean all tests, (salinity, phosphate, nitrate, ammonia, iodine, iodate, ca, mag, Kh, Ph,) perfect. Could never figure it out. Only guess was some stray current somehow. Who knows, good luck with everything!
I am a kid and my sister is old enough to know and my parents too. I don't think anyone would have purposely or accidently put something in the water. No one was home
It is unfortunate that you came home to this.I would lean towards your heaters though.Maybe they all kicked in at once and the tank got hot.This would cause the oxygen levels to go down.Combined with a Nori leaf that may not have gotten eaten right away? You could hould hold a service for the deceased.I would recommend burying them in the garden under a Lavender or other salt tolerate plant.Best of luck to you!
I don't know of anything other than velvet that will wipe out that many fish over night and you would of noticed velvet before all this, I mean this is a nice tank and is obviously observed frequently. I find it odd you hung a clip of nori and you came back and all of the nori eaters were dead.
I hung the nori routinely but I did it in the dark because I had to leave early. I belive the tangs died before I put the nori because I did not see a bite in it
Yes I know where they sleep and some died where they sleep. Some of the small fish that died I do not know where they sleep but half of my tangs died where they sleep while the other half was somewhere else. It could be of the current that pushed them somewhere else
Another theory: One of your larger tangs (like the naso) died first, the decomposing corpse triggered an ammonia spike, but the hardier fish survived it. Did you find the bodies intact or being eaten by your CUC? How much time (do you estimate) passed between when they died and when you found them?
How about the frozen food that gets fed? Has it possibly thawed and refrozen? Or possibly some was leftover at night and thrown in the next day? Perhaps 2-5 days before the fish loss. I have on rare occasions seen this work as a precursor to serious disease in an otherwise stable tank.