JW Pet Company 6-Inch Aircore Sand Airstone Aquarium Accessory

Bury these under the gravel, so the light won't grow algae on the stone and clog up the pores.

It IS a porous stone, so you'll notice it'll start to crumble after 6 months or more. I dug one

up that was about a year old and it broke in half, but hey, it's a stone.

If you want one that lasts longer get a plastic air wall style bubbler...