Not toxins. Gotta chip the rock where the foot is. Like that. Or find something that eats them. If the rock is smooth. Yeah you can scrape it. But if you leave some small frags. They will grow back.
I have scraped them off flat surfaces with little damage. But like everyone said, you have to get it all. You can also turn off all the pumps and cover it in a thick Kalk paste for about an hour. That should melt it away.