My smallest is a glass (glass sized), I keep my oscars in it. Not really, it's a pico planted with some cabomba and a (pest) snail. I love this little guy/gal now, so cute If I could just find some really snail infested plants I'd be happy. My next smallest is a jar, again, a pico planted, then a beanie box (pico planted), I had a really cool 1/2g but I didn't silicon up the crack properly. I'll get another one, that ade a really good pico planted.