Many problems here. Inverts will not tolerate low PH
, it needs to be above 8.0
Ammonia needs to be zero, most marine livestock cannot tolerate even small amounts of ammonia for very long, especially inverts.
Stars must be drip acclimated for several hours. Way longer than fish. That alone can cause their demise. CC
stars are very sensative to changes in water parameter and poor water quality. They also should never be exposed to air or be touched by our hands.
I would suggest that your take them back (now that they are out of the system) until the tank cycles properly. If fish can't survive in this tank, it is definately not ready for delicate inverts such as CC
Send you friend here, we can help them get set up properly.