Using a reliable Fluke 77 IV multimeter I have 20V AC when I put the black in a grounded terminal and the red in the tank. I get the same when I removed all wires. I also get 20V when I do the same in a plastic terrarium with saltwater, Phyto and pods and an air bubbler only.
I think the voltage is ok. The Canary Blenny is still super spooked; the larger fish are ok.
If it were a chemical like sunscreen or bug spray, I would think it would kill the things in the exile tank first since that was exposed directly. Also, The coral banded shrimp are fine.
I think I have a killer

I bet its the six line.

I see him stepping to all the chromis and the larger fish are antsy when hes near them.
Can six line take out larger fish like anthias?