Calcium levels won't have any direct effect on soft corals. Alk levels on the other hand would have some. The same can be said about 'stinging'. Soft corals can't sting like LPS. They battle each other with chemical warfare.
Though the last there could be an option, it is normal for soft corals to close up for some time as they 'shed their skin'. Once this is done, things are back to normal. This is one theory as to why there aren't many, if any, parasites that bother these types of soft corals.