I had a tank overrun with pond snails
. I think they hitched in with some plants although I had rinsed them before putting them in the tank. It took forever and I was using the blanched lettuce method. Finally, I got sick of the constant fighting with it and totally disassembled the tank, cleaned everything, resoaked the plants in bleach solution and then boiled the rocks for 5 minutes, reassembled everything, and still ended up with a few left. Before the boiling, i put the rocks in my bathroom sink (the wife LOVED that... not) and swished when aound in water so I could separate the snails from the rocks. I tossed all the snails I found out in the yard. Now, I havent seen any in a while but during the cleaning I found several hundred ranging in size from the head of a pin to 1/4 inch. Next time, it's an assasin snail for me.