Snails. Great creatures. They can sleep up to three years. They come in
on
plants, in the bags of substrate and through other sneakier means I've
been
unable to discover. They're asexual, so to multiply, all you need is two
snails.
That's it. Two snails will get you millions. They sell products like
snail-a-cide to kill a few of them here or there, but it's easier to keep
up
with tank cleanings and water changes. You can also make snail traps by
putting
a piece of lettuce or something in a film canister with holes in it. In
the
night, the snails will flock to it and you can remove quite a few this
way. I've
found that once you have snails in your tank, they're just about
impossible to
get rid of.

.......unless you put 2 or 3 Clown Loaches in there as well. I've got two
tanks, one has loaches & is snail free & the other didn't & so wasn't. I've
recently put some loaches in the second tank & they are committing
systematic genocide on the snail population therein (as intended!). Previous
to that I used to vacuum out as many as I could (several dozen at a time)
and
then stick them in the other (snail free) tank. The loaches in there would
make short work of them.

I.