Just as an update I got all of the fish in the QT since last night. I dosed it with ICH-X. The tang is looking much better. The tang and the clown fish are all doing well, though they ate less than normal today (but are eating).
My blenny on the other hand isn't doing great. He is very lethargic and didn't eat. Not sure if it's the transition or the velvet is hitting him harder. I can't see any visible signs of it, but my understanding is it could be in his gills. Thought about doing a fresh water dip on him to be safe, but if he's just stressed worried that might push him over the edge.