Bio-balls (plastic biofilter media)

Properties

In a system

• Engineered plastic (usually HDPE) shapes with very high specific surface area; Kaldnes K1 provides about 500 m2/m3 of protected surface, among the highest of common biofilter media
• Not a grow-bed medium, since plants don't root into it; used in a separate moving-bed biofilm reactor (MBBR) chamber or a static sump biofilter that supplements raft or NFT systems
• Density near that of water (about 0.94-0.97 g/cm3) so the carriers float and are kept suspended and moving by aeration in MBBR designs, or are weighted in static use
• Common pairing with raft systems, which have no biofilter capacity themselves; the MBBR chamber is often sized at roughly 10-15% of fish-tank volume
• Adds capital cost but reduces the grow-bed area needed purely for biofiltration, useful when grow-bed space is constrained but fish load is heavy

Notes

K1 (Kaldnes K1) is the common MBBR shape, and cheaper generic versions work equivalently. Avoid the very large golfball-sized rigid 'pond bio-balls', which carry far less surface area than properly engineered MBBR media at the same price. In an MBBR the carriers are kept tumbling by aeration so biofilm forms on their large protected internal surface.

Further reading

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