Why was there one snail in tank and now are baby snails?

It's likely that your single snail was a hermaphrodite and laid eggs! Many snail species are hermaphroditic, meaning they have both male and female reproductive organs.

Here's how it could have happened:

* Self-fertilization: Some snail species can fertilize their own eggs.

* Previous mating: The snail may have mated with another snail sometime in the past and stored the sperm, only to lay eggs later.

To prevent future baby snails, you can:

* Remove any eggs you find. Snail eggs are usually small and white, often laid in clusters.

* Consider a snail-eating fish. Some fish species enjoy snails as a snack.

* Change the water frequently. This will help to discourage egg-laying.

Enjoy your new snail babies! They can be fascinating creatures to watch.