How to Choose a Drum Filter for a Koi Pond

A drum filter is the heart of a modern koi pond: it strips out fine waste automatically before it can break down into ammonia. Choosing the right one comes down to how much water your pump moves, and how the filter is fed.

What a drum filter does

Water from your bottom drains and skimmers flows into a slowly turning drum covered in fine mesh. Dirt is caught on the mesh while clean water passes through. As the mesh loads up, the water level on the clean side drops, a float switch starts a short rinse cycle, and spray jets wash the waste straight to drain. The result is clean water with almost no manual cleaning.

Step 1: work out your flow rate

Koi ponds are usually filtered so that the whole volume passes through the filter every one to two hours: closer to one hour for heavily stocked ponds, two hours for a few small koi.

A 15 000 litre pond turned over every 1.5 hours needs about 10 000 litres per hour (10 m³/h).
A 40 000 litre pond turned over every hour needs about 40 m³/h.

Not sure of your volume? The pond calculator works it out from your pond’s length, width and depth.

Step 2: match the drum to the flow

Choose a drum whose rated range comfortably covers your flow, ideally with your flow in the lower half of the range so the drum is not rinsing constantly.

Model	Flow range	Inlets / outlets	Suits
PrimoDrum Drum 25	10 to 25 m³/h	3 / 2 x 110mm	Small to medium ponds
PrimoDrum Drum 35	15 to 35 m³/h	3 / 2 x 110mm	Medium ponds
PrimoDrum Drum 50	25 to 50 m³/h	4 / 3 x 110mm	Larger ponds
PrimoDrum Drum 65	40 to 65 m³/h	4 / 4 x 110mm	Large, heavily stocked ponds

All PrimoDrum drums are made in South Africa from marine grade stainless steel with a 70 micron woven stainless steel screen.

Step 3: gravity fed or pump fed?

Gravity fed is the preferred set-up: the drum sits with its water level the same as the pond, bottom drains feed it by gravity, and the pump sits after the filter, so it only ever pumps clean water. It needs to be planned when the pond is built. Pump fed drums sit above pond level and are easier to add to an existing pond. PrimoDrum units can be set up either way at no extra cost.

Step 4: add biological filtration

A drum removes solid waste, but beneficial bacteria are still needed to convert ammonia and nitrite. Either add a separate biological stage such as a Bakki shower or BiFilter, or choose a combination unit like the BiCombo 25 or TriCombo 50, which build the drum and a moving bed into one stainless steel unit. Finish the system with a correctly sized UV clarifier for clear water.

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