Bettas can do fine in that sort of set up (since they can breath air) and the snail, if it's not particularly large, wouldn't have a temendous impact on things so long as water changes are done . For other types of set ups , I'd think there would need to be a constant waterchange system in place to remove pollutants otherwise the water would foul quickly. Many Asian breeders use a constant change system which eleminates the need for filtration since all of the water is changed over the course of the day.

It should be noted that the concept of no waterchanges works well with tanks that are heavily planted and very lightly stocked, but they begin to lose their filtration abilities as stock levels increase. At some point disolved organics reach a point where they can begin to cause problems, particularly as stock levels increase. Cichlid tanks simply need waterchanges. They are far too messy and produce way too much waste for a planted tank (provided the cichlids didn't destroy the plants) to absorb . I have never been able to successfully keep cichlids and plants in the same tank, so waterchanges have been a way of life. Typicly I perform 80% weekly . While this isn't for everyone , this level of waterchange (along with my habit of light stocking) keeps pollutants from acumulating to significant levels. I've been doing this for quite a while and it works very well , though it is a bit of a chore when your tanks are over a hundred gallons but healthy fish are worth it IMO.

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