Sorry to hear Bill.
It seems like they all went over a little while? not all at once really? The ones that took longer...were they looking good and then went suddenly, or did some go and the others were looking bad and then went? I'm just trying to get an idea...I would think if it were a contaminant they would have all gone at once pretty quickly. But if not a contaminant...what the heck is it?????
Not all the fish that have died in this tank were in at the same time.
First to go was the juv Atlantic blue tang. about a week. Eating fine, swimming great. Then dead.
Drained over 50% of the water, cleaned all the equipment.
About a week or so later, I got my Wardii goby. He went in the tank. He was in for about 3 days or so when my filter on the mandarin's tank started leaking all over the place. I had no choice to move them, and all their LR, into the 40B. About 3-4 days after that, the Wardii died (about a week total).
Tested water, results were posted here. Nothing unusual. It should be noted that I don't have any of the other tests, such as copper, silicates, etc.
Since then, the mandarins have been in this tank without issues. Even game them supplemental frozen food that the LFS owner said that a lot of people are having great sucess with feeding to their mandarins. Worst case scenario, they didn't care for it. Not big deal.
Changed out some water (don't recall how much).
About a week later (the other night) the mandarins were gone.
It's gotta be contaminant. There's just no other thing I can think of. I doubt it to be stray voltage, as my hands are in this tank a lot and have never felt anything. Plus the only equipment in the water was a 300W heater (I'd feel that) a MJ1200 (I should feel that too) and if you want to count the HOB filter as "in" the water, then that too.
I just don't get it.