what is killing my coral bells
The black specks are excrement from insects in the trees overhead. Look there. This is not hurting the coral bells, however.
The larger brown balls may be galls, again falling from overhead. Look at leaves above your coral bells. This, too, is not harming your coral bells.
The third photo suggests the disease rhizoctonia web blight, which can plague coral bells: http://extension.umd.edu/hgic/rhizoctonia-web-blight-flowersgroundcovers