Round blue porous stone
Regular price
$3.00
Regular price
Sale price
$3.00
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/
per
This porous stone ball, 30 mm across, diffuses air in fine bubbles in an aquarium, a pond or an aquaponic system. It connects to standard airline tubing, 4/6 mm.
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The summary
- What it is: a 30 mm porous stone ball, 4/6 mm fitting.
- What it connects to: standard air tubing, the kind used with aquarium air pumps.
- How to choose: the ball oxygenates a single spot, the 20 cm disc covers a whole bottom.
- When to replace it: as soon as the fine cloud turns into a string of large bubbles.
A spherical diffuser that fits onto a 4/6 mm airline pipe
The round blue porous stone is a spherical air diffuser of 30 mm, fitted with a 4/6 mm fitting that attaches to the standard airline tubing of aquarium air pumps. It turns the airflow into a cloud of fine bubbles, released all around its surface. It should be replaced when the bubbles become large and uneven.
This porous stone ball measures 30 millimetres and its fitting is 4/6 mm, the standard diameter of the airline tubing used with aquarium air pumps. You slide it onto the end of the line and place it on the bottom, and the airflow becomes a cloud of fine bubbles instead of a jet.
The fitting
It measures 4/6 mm, the diameter of standard air tubing.
The shape
A sphere releases its bubbles all the way around, not just upwards.
Space
A 30 mm ball fits in a pot, a quarantine tank or a corner.
The sign of wear
Large, irregular bubbles replace the fine cloud of the first months.
🔁 The part that gets replaced
An air stone is a consumable. The mineral salts in the water crystallise in its pores and biofilm settles on top, until the day the steady cloud of bubbles becomes a string of large bubbles coming out on one side only. An acid bath reopens it once or twice, then the effect wears off and it is replaced. Keep a spare in a drawer, dry and in its packaging, because aeration matters most during heatwaves, when the water holds the least oxygen.
A two-outlet pump for two tanks
An air stone needs an air source, and its 4/6 mm fitting connects via the airline tubing to the aquarium air pump. Choose the twin-outlet version so you can run your main tank and a quarantine tank at the same time, because that set-up saves you from unplugging one to power the other. The pond aeration kit comes with porous stones of the same diameter.
📍 Where to place it in a tank
Place it on the bottom, preferably in a corner rather than under the filter outlet. The bubbles draw the bottom water upwards as they rise, so a stone placed opposite the filter sets the whole volume in motion instead of reinforcing an existing current. If you connect several, give each one its own line from a valve, because when they are connected in series the last one only receives what is left. The article on common mistakes explains why aeration matters, especially in hot weather.
A clogged air stone makes the pump work harder
A stone whose pores have closed up puts up growing resistance to the airflow, and the pump pushes against it to no purpose. Replace it as soon as the bubbles get bigger, rather than raising the flow rate to compensate. Keep spare stones stored dry in advance, because a damp stone that dries badly retains its deposits.
Technical specifications
The essentials
- What it is
- Spherical porous stone diffuser
- Diameter
- 30 mm
- Air fitting
- 4/6 mmThe usual diameter of aeration pipes.
- Colour
- Blue
To budget for separately
- Air pump
- 4/6 mm outlet
- Air pipe
- In 4/6 mm
In the box
- 1 round air stone, Ø 30 mm
Diameter and fitting taken on 20/09/2026 from the AquaKing page for the 30 mm porous air stone, reference B2020014.
Two diffusers, two surfaces
The same porous stone and the same principle. What changes is the surface that bubbles and the fitting that feeds it.
The diffuser size follows the size of the volume
An air stone oxygenates one point, a disc covers a surface. Where you place it matters more than the power of the pump.
| Diameter (mm) | Shape | Air fitting | Fits in a pot or a small tub | Covers the bottom of a pond | Plugs straight into an aquarium pump without an adapter | Price | |
|---|---|---|---|---|---|---|---|
| Recommended Round air stone, 30 mm, 4/6 mm fittingYour choice | 30 mm | Ball | 4/6 mm | Yes | No | Yes | $3.00 |
| Porous stone diffuser disc, 20 cmYour choice | 200 mm | Flat disc | 8 to 10 mm | No | Yes | No | $24.00 |
Round air stone, 30 mm, 4/6 mm fittingRecommended
The diffuser
Diameter (mm)30 mm
ShapeBall
Air fitting4/6 mm
Where it is placed
Fits in a pot or a small tubYes
Covers the bottom of a pondNo
Plugs straight into an aquarium pump without an adapterYes
Porous stone diffuser disc, 20 cm
The diffuser
Diameter (mm)200 mm
ShapeFlat disc
Air fitting8 to 10 mm
Where it is placed
Fits in a pot or a small tubNo
Covers the bottom of a pondYes
Plugs straight into an aquarium pump without an adapterNo
Diameters and fittings recorded on 20/09/2026, the 30 mm ball from the AquaKing page for its reference. Another diffuser in the shop: Cylindrical air stones, 50 x 50 or 100 x 50 mm.
Help choosing
Which stone for the spot you want to oxygenate?
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Frequently asked questions
6 questions
6 key questions
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