what are this grow on my rock

[kyowang]

 

[anemoneanatomy]

You have a severe infestation of vermetid snails, my friend

 

[kyowang]

You have a severe infestation of vermetid snails, my friend

Are they good or bad?

 

[anemoneanatomy]

That depends. Some species are spread faster than others, and some species are more aggressive than others. There are people on these forums who think they are neutral filter feeders, or even good, because they are kind of cool looking. If you want to stock coral or any other sessile invertebrates, however, I would say they are at the very least a nuisance species, and at worst an active threat. There's an accessible article about them here which cites sources if you want to read scientific studies.

I had a small outbreak a few months back that I contained using glue. Since then, when the occasional vermetid makes itself known, I snip its shell to the base with a nail clipper and then clip its shell in half to kill the organism.

Please be aware that no matter what method you use to kill them, they will not die if you just remove the part that projects away from the rock. The living parts of the snail are all contained in the spiral structure at the base.

 

[Dkmoo]

They will regulate them selves as your tank matures. This usually us the case in newer tanks that have high DOC/DOS.

It doesn't look like you have a lot coral yet so it shouldn't be too much of a nuisance.

Reduce your doc/dos should help. Either filter socks or skimmer

 

[Llyod276]

Do nothing like me. For some reason mine have all died off. This was back when I did few to no water changes and ran my skimmer at 12hrs if at all...

 

[Sharkbait19]

They release a mucus net that irritates coral. Bumblebee snails are supposed to help control them.