Net cups (raft / DWC beds)

Properties

In a system

• Not a biofilter medium itself; raft systems put plants in mesh cups suspended in flowing water and rely on the fish tank or a separate biofilter sump for ammonia conversion
• Best for leafy greens (lettuce, basil, kale) because the roots dangle directly in oxygenated water; fruiting crops with heavy root masses struggle
• Insulating polystyrene rafts keep water temperature stable through summer heat better than open media beds
• Cleanup between cycles takes minutes (lift the raft, rinse the cups, replant) versus the hours a media bed takes to drain and clean
• Requires a separately-sized biofilter (usually a moving-bed reactor or a small media-filled sump) to compensate for the lack of biofilter surface area in the bed itself

Notes

Cups come in 2-inch and 3-inch standard sizes; match to the rockwool starter cubes or expanded clay seedling plugs you'll use. Polystyrene rafts last about 10 years before UV embrittlement; cover any exposed top surface with paint or another insulating layer to extend life.

Sources

uvi-aquaponics-program, nelson-pade-raft-systems

Further reading

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