Hi. It's been over 5 years since I've had any tanks up and running. But recently I've been daydreaming of setting up a planted tank in a 20-gallon long. I don't think I want fish, and instead I'm considering shrimp, snails, or other invertebrates. My two priorities are this: (1) a peaceful tank--so nothing that eats live food, its own babies, or its tankmates; and (2) a sustainable tank--so nothing that will breed so much that it outgrows the 20-g. I had originally thought of cherry shrimp, but I hear that I'd soon have hundreds and would need to cull them somehow, or sell the extras, etc., and I don't want to deal with that. Ideally I'd like something a little more active than snails. Does anyone have any recommendations that might fit what I'm looking for? Thanks!