Disease in Tank?! Dying Fish

[Koolaidreef]

Hey MR,

Always heartbreaking to have one of your fish pass. I consider all of my animals family, and want to ensure I’m doing my best to keep them healthy.

My Scopas Tang seemed to get sick yesterday after I did a major filter clean. Everything was off for 2 hours or so. I noticed this morning he was not eating, and later in the day, he seems on the verge of dying.

Not sure if there’s some sort of parasite in the tank, as my UV has been off for 24 hours. I’d appreciate any input to save my other fish.

 

[Humblefish]

It looks like a bacterial infection: https://humble.fish/bacterial-infections/

 

[homegrowncichlid]

I'm thinking it was too hot, low dissolved oxygen level if pushing 85 or 86F, for 2 hours. Also the massive nutrient release from the cleaning may have caused a bacterial die off, also sucking up oxygen/ releasing endotoxins or ammonia, or he ate something poisonous in the filter, I've had a tang accidentally eat a flatworm, but he died instantly.
just some thoughts, since there's no way for anyone but you to figure it out.