Yep the black spots are most likely from him hosting something he shouldn't be (mines hosting zoas) I figure if it hurts he'll learn to avoid them and the coral doesn't seem to mind either so Im not to worried. Sounds like yours is either hosting the gsp or Kenya tree, you should try and catch him in the act
These are the filters I got if you're interested
http://m.ebay.com/itm/Gel-Filters-f...3D262054708619&_trksid=p2056116.c100408.m2460
These are the filters I got if you're interested
http://m.ebay.com/itm/Gel-Filters-f...3D262054708619&_trksid=p2056116.c100408.m2460