I have been curious about this for some time, but never got around to asking if anyone knew.
Every 4 to 6 months I completely clean my 120 gal tank. I mean removing everything and cleaning everything. When I get to the filters I am always amazed there are snails in the filters. My only guess is that they come in on new fish. Could that be right? I never see them in the tank only in the filters. I don't have live plants so I'm pretty sure they didn't come from there. I use tap water so they didn't come from there.
Does anyone have a better theory about the magically appearing snails? And why don't they migrate to the tank?



