I've found that wrasses cannot eliminate pyramidal snails from a tank. This is because the snails are nocturnal whereas wrasses are diurnal (sleep at night like us). So your wrasse is having sweet dreams when most of the snails are out and causing havoc.
The only way to eliminate the snails is careful manual removal over the course of several weeks.
Take the clam out with some tank water after lights out for a few nights in a row and scrub/remove as many of the little buggers as you can as quickly as you can. Be sure to get their eggs as well. Continue doing this every so often until no further snails are present. It took me a few months to get rid of everything (knock on wood) and I still do a check every few weeks or so.
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