525,
I've never owned a Blasto. IF I was told that what you pictured was a Blasto that was having problems... and asked to help figure out what the problem was... the only thing I would have to compair it to would be when I had a Bubble Coral.
The Bubble Corals have a similar underlying skeleton, that has the hard "ribs" if you would. When those ribs would poke thru the "meat" of the coral... they would get infected... and soon lead to problems for the coral.
Extream care was then needed to ensure water quality stayed as good as possible, and anything that may possiblly be irritating that place on the coral removed.
Please take this information as being from someone that has NO experience with Blasto's, but hopefully will spur the input from someone that does for you!