I have a 1 gal on my dining table that has no heater or filter and only gets sunlight. Just plants and snails. I only do a 1 cup water change when I think of it. No ferts on either, no CO2.
I've had slighty larger tanks with just the same set up and with a betta. Just do water changes in a semi casual fashion, wipe the sides down inside once a month.
For some reason, these tanks never have had algae problems...