Need help diagnosising quickly

[Sorcha2]

So Monday I got up my yellow tang was on the bottom head facing down barely able to move and breathing a bit labored. Came home for lunch and he was died. Tuesday morning fish all seem fine. Tuesday lunch my royal gamma is missing and hasn't been seen since. Today my mandarin perfectly fine in the morning, lunch time heavy breathing, pale around the head, exhuasted, hermit crab moving towards him like he's a snack.
Water parameters all seem fine and normal for tank tested Monday and today. I run carbon in canister filter and an airstone becuase of old habits from freshwater. The tank is 15months old. The only new fish was the tang added two weeks ago. Everything else has been in there for a minimum of 8months. It's a lightly stocked tank. I'm at a loss. Best I can figure is maybe a bacterial infection? Ideas, suggestions for treatment greatly appreciated.

 

[ScooterV]

Do you quarantine? The tang added two weeks ago could have brought in any number of things. Any pictures?

Also, what parameters are fine and normal? What were the actual results? Tank size and what light bio-load is?

 

[HotRocks]

Agree^^^

Did you QT they yellow tang?

 

[Sorcha2]

I didn't quarantine it but I only buy from a store that quarantines with copper and hypo salinity. I checked nitrates, natrites, ph, gh, kh, salinity, and temperature. Stocking level 4 small fish in 65g. I already ruled out all the common suspects, ick, velvet, flukes, ammonia poisoning. When I got home from work just now my mandarin was died as well. Looking online the only thing that I've seen that really seems to fit the symptoms is Mycobacteriosis.

 

[JumboShrimp]

I’d bet my bottom dollar that the new Yellow Tang was your silent assassin. So very sorry.

 

[Big G]

The fish industry supply line has velvet and a very bad bacterial infection situation these days. Both are quick killers and often without showing much if any visible symptoms until too later or not at all. I know you posted the LFS does QT, but in truth, the only QT you can trust is your own. Think of it this way. You QT a single or a couple of fish and dose, observe, and care for just them. Multiply that by a LFS with hundreds of fish and perhaps dozens that are in their version of QT. It's not the same care you would give. IMO

 

[HotRocks]

The fish industry supply line has velvet and a very bad bacterial infection situation these days. Both are quick killers and often without showing much if any visible symptoms until too later or not at all. I know you posted the LFS does QT, but in truth, the only QT you can trust is your own. Think of it this way. You QT a single or a couple of fish and dose, observe, and care for just them. Multiply that by a LFS with hundreds of fish and perhaps dozens that are in their version of QT. It's not the same care you would give. IMO

This^^^ My thoughts exactly.

 

[ScooterV]

@Sorcha2 I made my initial post so you could get more info I knew some of the experts would likely ask for or need to save you time.

However, on the topic of any LFS doing a QT it's usually meaningless unless you KNOW exactly how long the fish was there, if anything else was added to that system, how long it was treated, etc. And it would be a rare LFS that would segregate a new fish for a month, or more, before selling it. That tang may have been there a day, or a week. The copper they maintain may be sub-therapeutic but it keeps the fish "looking" ok.

Nothing against that LFS, it's just simply something they can't do THEN, like me, even knowing better we still make mistakes at times!! It's a minefield!

From my own recent experiences I would bet on bacterial or velvet. In past years I never recall issues so often as today