The SPECK 4‑9 mm Koi Gravel Filter Medium is excellent for use in ponds and gravel filters where larger particle size is preferred for improved water flow and reduced clogging. Its 4‑9 mm gravel offers a sturdy support layer beneath finer media or can be used alone for gravel filtration. Supplied in a 40 kg bag, this washed and inert material is safe for koi and other aquatic life, allowing for biological filtration while maintaining clarity.

• Key Features

• Particle size: 4‑9 mm nominal size
• 40 kg bag – ideal for gravel beds, filter underlayer, or bulk applications
• Washed and graded to remove dust and fines
• Rounded/pebble texture to promote even water flow
• Stable, inert material with no coatings or additives; safe for aquatic ecosystems

✓ Benefits

✓ Reduces clogging and pressure drop in filters by maintaining open flow paths
✓ Acts as an effective support layer under finer filter media
✓ Enhances biological surface area for beneficial bacteria colonisation
✓ Long‑lasting with minimal maintenance; cleans easily
✓ Fish‑safe, non‑toxic, and stable across pond chemistry

Technical Specifications

• Particle Size: 4‑9 mm

• Bag Weight: 40 kg

• Typical Use: Under‑layer support gravel, gravel filter beds, or coarse filtration zones

• Porosity & Drainage: Higher permeability compared to finer gravels or sand

• Usable Lifespan: Many years; replacement only necessary when compromised by excessive fines

What You Get

1 × 40 kg bag of SPECK Koi Gravel Medium (4‑9 mm size)