An air stone is a porous block or disc, made of mineral, ceramic or sintered material, fed by an air pump through tubing. Air forced through it emerges as many fine bubbles. The bubbles themselves add some oxygen, but their main effect is circulation: they keep the solution moving, bring water to the surface where it exchanges gases with the air, and prevent stagnant zones.
In practice
In DWC and RDWC, air stones run 24 hours a day. A rough rule many growers use is about 1 L/min of air per 4 L of solution, or morebeing reviewed. Clean or replace stones when bubbles become coarse or uneven, since mineral and biofilm build-up clogs them. Place the pump above the water line, or fit a check valve, so water can't siphon back into the pump if it stops.
Aeration only works well in cool water; warm solution can't hold much oxygen however hard it is bubbled.
Don't confuse with
- Water pump: moves solution; an air pump moves air.
- Venturi or oxygen injector: other ways of raising dissolved oxygen.
