Be nice to them
Algae that is attached, like BBA, will also do this if the BBa dies or is pulled off of them.
I do not think many hobbyists know much of the shells and how they are formed on mollusk.
It's a favorite test question when I taught Diversity form and function for Bio majors.
I do find it a bit odd there's never any talk about it on FW invert forums.
Although I'm probably not looking in the right spot?
Regards,
Tom barr