Types of Filters

Koi pond filters come in several types, and many ponds use a combination of them, these have largely changed over the years thanks to the innovation of several high end Koi equipment manufacturers. The main categories are:

1. Mechanical filters

These remove solid waste (fish waste, uneaten food, leaves, and debris) from the water.

  • Settlement chambers (vortex filters)
    • Use slow water flow to let heavy waste sink to the bottom.
    • Low maintenance and effective for larger ponds.
    • Often paired with biological filtration.
  • Sieve filters
    • Use a fine mesh screen to separate solids from water.
    • More compact than settlement tanks.
    • Good for removing waste before it breaks down into ammonia.
  • Drum filters (rotary drum filters)
    • Automatic mechanical filters that use a fine screen and rinse themselves.
    • Very high performance and popular on large or high-quality koi ponds.
    • More expensive and requires power/control equipment.
  • Foam/sponge filters
    • Simple mechanical filtration using foam pads.
    • Usually used on small ponds, quarantine tanks, or as extra filtration.

2. Biological filters

These convert toxic fish waste into safer compounds using beneficial bacteria.

  • Moving bed filters (K1/Kaldnes-style media)
    • Use floating plastic media that constantly tumbles with air.
    • Excellent oxygen levels and very low maintenance.
    • One of the most popular modern koi filtration methods.
  • Static biological filters
    • Use fixed media such as plastic chips, brushes, or ceramic media.
    • Good bacteria colonise the media.
    • Require occasional cleaning.
  • Bakki showers
    • Water trickles over stacked trays filled with media.
    • Highly oxygenated and excellent for koi growth and water quality.
    • Common on serious koi ponds.
  • Trickle towers
    • Similar to showers but often smaller.
    • Improve oxygenation and biological activity.

3. Pressure filters

  • A sealed filter unit where water is pumped through filter media.
  • Can sit above or below ground.
  • Often includes a backwash function.
  • Convenient for smaller koi ponds.
  • Less ideal for heavily stocked large koi ponds because they can clog quickly.

4. Bead filters

  • A pressurised vessel filled with thousands of small plastic beads.
  • Provides both mechanical and biological filtration.
  • Compact and effective.
  • Needs regular backwashing.
  • Often used where space is limited.

5. Plant-based filtration

  • Bog filters / wetland filters
    • Water passes through gravel and plants.
    • Plants absorb nutrients.
    • Can provide excellent polishing but need space.
    • Usually used alongside mechanical filtration for koi.

6. UV clarifiers (not technically filters)

  • Use ultraviolet light to kill free-floating algae.
  • Helps prevent green water.
  • Does not remove fish waste or replace biological filtration.

Common koi pond filter setups

Small pond (up to ~5,000 litres):

  • Pump → pressure filter/bead filter → UV → pond

Medium pond (~5,000–20,000 litres):

  • Bottom drain → sieve → moving bed filter → UV → pond

Large/high-quality koi pond:

  • Bottom drains → drum filter → moving bed → UV → Bakki shower → pond

For koi, the best systems usually separate the jobs:
mechanical filtration first (remove waste) + biological filtration second (process ammonia/nitrite)

There are many variations but all have the same goal in keeping the water quality in top notch condition for your Koi.

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