Sounds like it could zoa pox. There is an article on it on Reef Central. It's in the zoanthid forum.
Can you post pictures of the white spots?
Are the polyps sitll opening up? Or do they stay closed?
There is also a very informative article on the treatment of these ZoaPox on ZoaID.com
You are not alone in this battle.
ALOT of people are dealing with these white "bumps" on there zoas.