Ive heard that a lot of Anabantids (guoramis in this case) will destroy snail
populations

LeighMo wrote:

It's the kuhli loaches. They wreak their havoc after the lights are out,
which is why you never see them at it.

I suspect you are right. I found this on the Aquahobby Kuhli Loach page:

Kuhli Loaches are a resilient species that, while nocturnal, will do well at
most any time of day in a high current, high activity tank. Never had a problem
with them being jumpers, however they are fast swimmers and love swimming up
against a downcurrent. They are also a great way to reduce the population of
small snails that can quickly overrun your tank.

Leigh

http://www.fortunecity.com/lavender/halloween/881/