Thanks everyone! I highly recommend active dither fish now that I've seen the difference in movement around the tank from before/after adding them. When he was by himself, he would pretty much camp out dead center of the tank and just hang out in the flow.
With the SDs in there he's constantly swimming circles around the tank with them or chasing them off, and he doesn't notice movement outside of his tank as much as he did when he was alone. He also feeds a lot more aggressively now that he's got competition for food in with him.