how small can you go???

I understand now what is being said by adding an airstone. It could help with water movement, but I also think that it would cause some salt creep that isn't necessary. If there is live rock in there, then you could get away with no filtration as long as you are doing enough water changes. I still think that a HOB filter would be a good way to go though.

 

as yu can see in my thread with the seahorse tank setups, i have two just like this tank and a slightly larger one. the air pump surprisingly doesnt add much salt creep, but if you have the lid on the salt tends to build up right between the tank and the lid. i would suggest just not having the lid on anyway to have better air exchange and to keep ph within range.