I am thinking about the same thing (all I have is a recently set up 55 planted, diy co2 and 1 female guppy), to get around not being allowed to have more tanks in the house. Google at Diana Walstad, she is awesome and has been doing a lot of this. It seems if you are careful 1g is plenty for shrimp and 5-12 plenty for small fish (harlequin rasbora, etc), even if you don't have an airstone, forget about a filter. I know this sounds nuts after so many people screaming BIGGER for so long, but pico and nano setups are really good with minimal maintenance ( as long as it is appropriate and regular) in both fresh and saltwater. Google planted vase and look for the same on Youtube. People are getting unbelievable bioload, stability and self sufficiency out of tiny setups.