Not many people know this, but water snails have secret powers of teleportation. That's how they appear everywhere, including in quarantined, snail-free tanks. They teleport
I adore all my snails and don't mind having them in the least. I am actually thinking about having a snail-only tank for the next lot of blond snails I get in..
I have ramshorns (the babies are so adorable), ponds, Waterhouse snails (native Aussie trapdoor type), Malaysian trumpets and -- I think - I have an assassin snail or two as well. I don't mind having a bajillion, as I keep up frequent water changes to cope with the bioload.
My first shipment of adult blond snails died, I think it was the soft water they were in -- but I found baby ones in a completely different tank, one I am sure the adult snails were never in. They are definitely teleporting!