update...
Fire fish perished...
I'm not sure but live brine shrimp may be to blame. I strained them but used the same net.
The store I bought the fish from used low solution Cu in their tanks and maybe after that wore off, whatever was in the water from brine shrimp took off.
The mandarin in the tank is fine so I'm guessing it was some sort of disease that their slime coat protects them from. (I purchased the Mandarin four days after the fire fish thinking she is pretty much immune to everything anyway). I decided to turn that tank into a peaceful tank and added the LR for the Mandarin.
Since the Mandarin is fine I will just let her have that tank and start a new QT. I don't think it counts as being fallow if she is in it...(she is eating frozen foods).
It could have been any number of newbie things! It's been a while since I have started purchasing new fish!!!
It could be that I decided to convert the tank to a FOWLR too soon. I added LR from my DT only three weeks of QT. My DT may have a disease in it that the cleaner shrimp keeps in check and adding the LR could have introduced it?
At any rate I'm going to bleach the nets and bucket and HOB filter and anything else that was used for the fire fish. The only addition to that tank will be a cleaner shrimp.
I will start a new QT and only put a PVC pipe in it if I decide to buy fish again.
Let this be a lesson for all



(Not that anyone else would have done any of these things in sequence lol!)