Wow, that's a lot of stuff for a 29gal never mind the 20 they came in. I would continue with the wafer changes and post half the fish in the for sale section or just give them away, especially the yellow tang.
I'm not sure if more smaller water chages a few times a week would help vs one large one once a week, but you can give it a shot.
Also if you want to have corals you should think about getting rid of the CC stars.