The signs you've indicated are not in favor of good news sorry to say. You should attempt to adjust the salinity but don't exceed much more than 0.001 SG
The easiest way to allow the salinity to come up with less impact on the animals is through evaporation. It allows the animals to acclimate gradually instead of all at once. After the salinity (SG
) desired is reached, simpley top up the tank with new SW
that is of the same salinity.
Unfortunately once necrosis has started there's nothing you can do except play wait and see, they may yet recover. Just be sure there is nothing in the tank that will pick at the area's of the star, specifically shrimp.