Hey... I am a newbie myself and, from my research, I understand that airstones are NOT recommended for saltwater tanks. These are the reasons I found:
1- they do not provide the needed oxygenation in a tank.
2- they cause the pH to be constantly unbalanced.
3- they cause a lot of salt to form at at the surface where it bubbles. This could throw off your salinity.
4. They clog up easily. Therefore, they shouldn't be depended on as a major aeration system.
My suggestion is this: Convert this tank into a betta bowl and save to purchase a tank where you can set up a proper filtration system. In my humble opinion, by doing the Pico aquarium in this setup, you may be setting yourself up for failure. Place an airstone in a freshwater tank, not a saltwater one! I admit they are cool. However, you do not want to place the burden of aerating your tank on one of these. It was not designed to do that job!!!
By the way- I think you have a cool idea! It's the wrong setting, though.... Just my 2 cents....
36- gallon bow front FOWLR established on 11/1/14 with
1 blue- green Chromis, 2 bi- colored Chromis, 3 black and white Oscellaris clownfish, 1 orange and white Oscellaris clownfish, 1 Banggai cardinalfish, 11 Turban snails (1 died), 6 hermit crabs, 3 peppermint shrimp, and lots of love....