Brent they are plankton feeders and is why they are responding to brine shrimp. I would suggest to get some coral plankton food also food an target shoot them. I will add they are very heavy eaters and single a WP can filter 100's to 1,000's of gal of seawater a day depending on size.
pretty much nothing goes with them. no rocks, no corals no anything that they can bump into and would injure them. you have a species only tank at this point.