The shark has to go. If your quality is good it will survive and outgrow the tank in short order, if it's not so good it will die pretty quickly.
As far as ick goes , you have 2 real choices, copper or hyposalinity. Copper will kill everything except the fish, and some bacteria, hypo might well kill the 2 starfish and the anemone. Look on th web or in a book for fuller descriptions, or search in here, the treatment description is quite long. For hypo you need to take the salinity DOWN to 1.012 over a couple of days, and this has to be accurate so you need a refractometer or a decent floating hydrometer NOT a swingarm. The only meds I've heard work are I tihnk octozin, (Not available in US?), and Kent RX-P which to work needs high alk (11 +) and a decent skimmer and is not 100% invert friendly.
Really to fix this the most effective route is copper in a dedicated hospital tank, and NO FISH IN THE DISPLAY FOR 6 TO 8 WEEKS.