Question about spirorbid worms

[Leaellynasaura]

I have many of these growing on the glass in my coral quarantine tank and I fear they will soon grow in my much larger display tank. My question is about the material their shell is made out of. Is it equally hard as glass or more hard? Currently I use a plastic scraper to try to get them of the glass before using a mag float to remove algae out of fear their shells will scratch the glass. This is a major pain and makes me put off the task. Is this a valid concern? The thought of using the scraper in the display tank makes me sick to my stomach.

 

[saltyfilmfolks]

The shell is primarily calcium with a few other tings thrown in.
It's softer than glass.

I use a metal bladed sacraper a few times a week in my glass tanks. The plastic ones are fine too.