I'm fairly new to the Nano tank game myself (Though I've done larger marine tanks in the past) but I thought I'd share a bit of my current project with you.
I custom built my own Nano tank which is just shy of 9G. Rather than go the filter route I used a second 10G glass tank as a refugium (biological filter). The important thing here is that you need to look at your overall water displacment. For my 9G tank I have 19G of displacement, minus rock, sand etc... This helps me keep the water changes down and gives better balance to the overall setup.
The 10G glass tank was $10 and my pump was another $18. You'd need to add some sort of overflow to your main tank. Personally, even if you just had a 5G refugium/sump I think it would be helpful.
Anyhow, for my 19G of displacement I currently have two O. Clowns and one CopperBanded Butterfly. The butterfly is a baby but I've been catching some flack on other msg boards about having him in such a small tank. Additionally, I have a serpent starfish and a small cleaner crew (4 snails, 2 scarlet hermits, 2 blue leg and 2 red leg hermits). I fully believe that I could still add some more small stuff. I've been considering some green chromis as they will school together which is kinda cute to watch.
The last thing I'll leave you with is that I've also got a good amount of Macro algae in the refugium (both Chaeto and Calupera). These plants suck up the nitrates and help keep the tank in balance.
To date, my setup has been more stable than I anticipated and the cost of my nano (while higher than a stock glass tank) was still well within my budget.
Here's a quick fish photo:
Good luck & let us know how it goes.
