kush wrote:

a) Most likely, your fish ate them.
b) Snail-specific disease outbreak exacerbated by population explosion.
c) They crawled out of the tank and they're between your mattress and box
spring waiting for you to turn out the lights...

I vote for c, but a is most likely. Another possibility, or everyday occurance
in my tank, is that they are all in the canister filter living the good life
with lots of food and no preditors.