Bio-balls (plastic biofilter media)

Properties

In a system

• Engineered plastic shapes with very high specific surface area, 450-800 m²/m³ depending on the design, the most surface area of any common biofilter media
• Not a grow-bed medium; plants don't root into it. Used in a separate moving-bed bioreactor (MBBR) chamber or in a static sump biofilter that supplements raft or NFT systems
• Floats; needs to be contained in a screened chamber with aeration to keep moving in MBBR designs, or weighted in static use
• Common pairing with raft systems where the rafts themselves have no biofilter capacity; sized at about 10-15% of fish tank volume
• Adds capital cost but reduces grow-bed area needed for biofilter purposes alone; useful when grow-bed space is constrained but fish load is heavy

Notes

K1 (Kaldnes K1) is the common MBBR shape; cheaper generic versions work equivalently. Avoid the very large 'pond bio-balls' (golfball-sized rigid plastic): those have a third the surface area of properly engineered MBBR media at the same price.

Sources

kaldnes-biofilter-spec, wilson-lennard-aquaponics-handbook

Further reading

• Building a media-bed aquaponics system
• Aquaponics water chemistry: balancing pH for fish and plants