It is possible. I have a nine gallon aquarium, heavily planted. I also have a deep sand bed, tho' it's a freshwater setup. Currently I'm using some sintered glass biomedia and floss in a quick 'n' dirty filter but I only need it because I'm raising multiple generations of Endler's Livebearers so I feed six times a day.
Without all the fry and extra feedings, I have no need of filtration except for some floss to polish the water and to circulate it for gas exchange at the surface. With fewer fish, I could dispense with the circulation - I've a friend with a planted tank, deep sand bed, and a few dwarf puffers, and no powerheads or filters.
My nitrates are very steady at 10ppm and prior to the Endlers fry, 0ppm ammonia and nitrite. I very very rarely do water changes.
Read Waltstad's book "Ecology of the Planted Tank." Between that and my mentor's input on using freshwater deep sand beds, I've made a nine gallon nano pond.
Interestingly, the Walstad demonstrates that the majority of aquatic plants show a marked preference for ammonia, followed by nitrite, followed by nitrate. Terrestrial plants prefer them in reverse order.
Mulm sinks down through the sand as it disintegrates and reaches the anaerobic level, where denitration (an many other bacterial processes) generates nitrogen, carbon dioxide, and other gases which bubble up from time to time quite harmlessly. I NEVER vacuum.
To keep the sand from going completely anoxic, I've introduced malaysian trumpet snails and california black worms, which burrow and help water to circulate deeper into the sand.
Most posts seem to recommend lots of filtration and water changes and gravel vacuuming. To me, that style of tank is too sterile and doesn't have enough going on in it. Fish are great, thats why most of us keep tanks, but a fish in an ecosystem for context, to give the fish things to nibble on, to hide in is to me a whole lot more interesting. I'd say the work needed for either is about the same, but I'd rather be aquascaping, trimming plants, than vacuuming gravel and cleaning canister filters and changing water.
I dream of getting a 100gal and creating an amazon oxbow lake biotope or something very low circulation with discus or angelfish plus LOTs of teeny, little fish, shrimps, worms, etc.
