Whether or not you have thousands, depends on the type of snail.
The most common reason for snails is getting new plants - almost always have snail eggs or itty bitty snails hiding in them and it can takes weeks for them to come out of hiding, especially because they are mainly nocturnal.
Snails will really only proliferate like crazy if you overfeed (thus giving them lots to feed off and ideal breeding conditions) and don't vacuum the gravel well enough. Most snails you'll find randomly in your tank are asexual, which means it only take one snail to make a million. Mystery snails are not so much considered pests because it takes two to tango and they lay eggs, which can easily be removed.
I have a couple snails in my 55g because they are excellent for digging up the sand and reducing possibility of packets of poison gas.
If you feel you are being overrun, it's best to avoid meds, which can harm fish, and use the old lettuce/cucumber/zucchini slice at night & remove in the morning trick.
LoL. I think that covers it.
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I've moved your thread to the snail section of the forum.
Usually they're plant snails.