Help please

[alexmisk]

I have had a salt water aquarium for 2.5 years and last year I noticed that I have some sticklike growth on my live rocks. I took out the rocks and cleaned them, that is when I noticed them. They have also begun to grown on the shells of my snails. They are approximately ¼ of a inch long and have a hard outer shell. When the sand in my aquarium is stirred up you can see a sort of string coming out of the tube. They also tend to grow back stronger every time I try to get rid of them.
If anyone has had the same problem, could you tell me how to reduce the amount of them in my aquarium or how to get rid of them completely?
Thanks for your help.

 

[Myrddraal]

They're probably vermetid snails. You can pry the entire animal off the rocks, I usually use a fingernail. If you just break the tubes it won't kill them. I've also heard of people supergluing the tube shut to kill them. I don't know of anything that won't nuke your entire tank that will kill all of them at once.