PHEW. I dodged a bullet. Everyone is alive, and acting pretty normally now. The breathing is a lot slower, and they are swimming around like they used to. I guess one good thing that came out of this is that my clownfish are more active since the tang is not giving them a hard time anymore.
I'm thinking this was oxygen related, not sure exactly what happened but I'm going to give the powerhead a good cleaning and cautiously try it again in a few days. It's just hard to believe that adding a powerhead may have caused it.
Thanks for your advice everyone.
Sent from my iPod touch using Aquarium Advice