Waste sinks. A bottom drain removes it from the lowest point of the pond and carries it to your filter before it rots into ammonia, which is why every serious koi pond has at least one. Which drain you need depends on how your pond is built and how it is filtered.
Why a bottom drain matters
Uneaten food, fish waste and leaves settle on the floor. Without a drain they break down into ammonia and sludge, cloud the water and stress your koi. With a drain feeding your filter, that waste is removed continuously, so you should never need to empty the pond just to clear out sludge.
50mm or 110mm?
| Size | How it works | Best for |
|---|---|---|
| 50mm | Connected directly to the suction side of a pump | Smaller ponds with pressurised filtration (sand or bead filter, bio filter and UV) |
| 110mm | Feeds a gravity filter chamber or sump, with the pump after the filter | Koi ponds with a drum filter or gravity system; much higher flow |
Concrete pond or lined pond?
- Concrete ponds: the drain is cast into the floor. See the 110mm concrete bottom drain or 50mm concrete bottom drain.
- Liner ponds (fibreglass, plastic or rubber): the liner is clamped between flanges for a watertight seal. See the 110mm liner drain or 50mm liner drain.
Special drains for special jobs
- Diffuser drains add an air diffuser around the drain. The rising bubbles push waste towards it and add oxygen at the bottom of the pond. Available in 110mm and 50mm.
- Conversion drains turn an existing gully drain with no dome into a proper bottom drain, adding the anti-vortex dome that stops fish being drawn towards it. 110mm conversion drain
- Surface-mount drains are for concrete ponds built without a drain: the pipework runs on the surface and draws water from just above the floor, without breaking into the concrete. 50mm custom drain
- Stainless steel drains, such as the Japanese-style PrimoDrum bottom drain, sit flush with the floor so they cannot injure koi, and their grid keeps leaves out of the pipes.
Planning tips
- Slope the pond floor gently towards the drain so waste collects there.
- Larger ponds usually need more than one drain to cover the whole floor; ask us for a layout.
- Pair the drain with a surface skimmer or weir so floating debris is removed too.
Building or upgrading a pond?
APA Koi designs and builds koi ponds around correct depth, bottom drains and filtration from the start. See our pond services or WhatsApp 074 404 4539.