One gallon jar will hold a dozen snails. These are Magic Snails, which can grow quite large.
I'm no expert at this, our snails did not visibly grow, and we had them only a few months, because it was Kevin's job to change the water, and it got too hot the last time he changed it, and the snails all went belly up.
We never could find a thing they'd eat, other than algae from the jar, and that was very little.
They did not like algae pellets, it just fouled the jar. They did not like vegetables put in, they ignored them. They kept the jar squeaky clean though, and they moved around.
There are all kinds of complex systems for raising snails, but it really IS just as simple, as giving them water, and food, in a jar.
They will come to the surface for air as they need it, there is no need for a bubbler, they will meet their needs by moving.
We know of TWO systems that you can use, that are just jars.
1. Use a glass gallon jar, and you WILL need food inputs. Change the water either weekly, or monthly, depending on how many snails you have in there, and how big they are. Do a TWO THIRDS water change, don't change it all, and put in room temp water.
2. You need about a dozen glass jars, and a sunny window where you can line up the jars so they are in the sun, where they can grow good algae. Fill them to the top of the straight part of the sides, with NON-CHLORINATED water, and let them get good and green. Our friend uses Quart Jars, for TWO snails. He puts them into a nicely greened up jar. He says the larger ones will clean that in a day. If they can't quite clean it, you know you have enough. He says he NEVER changes the water, he just lets the algae eat the snail trail, and he lets the snails eat the algae. He has done it for four years, and his snails grow fairly rapidly. When the snails get too large, he sells them for about $40 each (they are VERY large).
You don't get anything usable out of raising snails, other than watching them grow. But Magic Snails are edible, and they do have a resale value, though it is slow to raise them.
There's also the potential for an algae crop here, but it is scut work.
You grow the algae in quart jars, and pour the quart jar of green water into a silicone or teflon lined cake pan, and set it under a fan to evaporate the water. You keep adding quart jars of algae until you have a thick enough layer of dried algae to scrape out.
Raising snails need not be complicated. It can be quite simple.
Aquaponics Anywhere is located in the United States.