Is one gallon enough for 3 snails?

[EmmaW.]

I recently purchased a new filtered tank for my three snails, as their old unfiltered tank stunk. It is one gallon, and I've noticed that my three snails (Gold Mystery, Blue Mystery, and Black Racer) move around much more in this tank, but it is smaller than my previous 1 and a half. Why is that? It it because this filter has a filter?

 

[Delapool]

Could be looking for food more, particularly as new but just a guess.

I must confess I find snails put out an incredible amount of waste and either lots of gravel vacs or bare bottom tank. The bare tank doesn’t look as nice but super easy to clean.