Snails releasing unusual white stuff

[Kryten]

If they are anything like the conical shaped snails that I had, with an opening right in the top of the shell, they reproduced and grew quite easily. Eventually though, most of the population was wiped out by my peppermint shrimp once they ran out of aptasia. However, I now have some new snails growing in my tank which look to be turbos - not sure which variety they are - got them from Aquagiant. They are surviving due to growing up on the safe side of my wall to wall overflow.