Your snail will likely do just fine with the filter you already have. Betta fish do well with sponge filters and other low-power filters. They are not the best swimmers and therefore hate a strong current. Your snails have the same needs! Snails don't swim like betta fish, but a strong current would easily move them. If you have a sponge filter or another low-pressure filter in your betta fish tank, you don't need to make any changes.