Application
Box Welded Koi Pond Liners
Koi ponds demand precision. A box-welded liner fits perfectly from day one — no creases, no trapped corners, no excess material. Just a clean, professional finish.
Why choose a box welded liner for your koi pond?
Zero creases at the corners
Koi are sensitive to sharp folds where sediment collects and bacteria thrive. A box-welded liner has no folded corners — just clean, welded joints.
Exact fit for any depth
Koi ponds are often 1.2–1.8m deep. We manufacture to any depth — and the liner fits without any excess material to trim or fold.
Drawing approval before manufacture
Every liner starts with a technical drawing you sign off. No koi pond liner is made until you have confirmed the dimensions are correct.
Why koi ponds demand a better liner
Koi are sensitive fish. A creased or folded liner corner creates a pocket of trapped, poorly circulated water — exactly where nitrifying bacteria fail to colonise and where detritus accumulates. Over time, those pockets become a chronic water quality problem that no amount of filtration fully compensates for. A box-welded liner has no folds. Every surface is flat, every corner is welded clean, and the full pond volume circulates as intended.
Material grade recommendation
We recommend our 1.0mm heavy-duty grade for koi ponds. At this thickness the liner resists abrasion from the fish themselves, withstands the mechanical stress of pumps and bottom drains, and provides additional protection at the weld points over the long term. Both EPDM and Butyl rubber are available at 1.0mm — either is an excellent choice for koi. The 0.75mm standard grade is adequate for many pond types, but for a koi pond the additional robustness of the heavier grade is worth the modest price difference.
Depth and bottom drains
Koi thrive in deeper water — the recommended minimum depth is 1.2m, with 1.5m to 1.8m preferable for serious keepers. We manufacture box-welded liners to any depth, including ponds exceeding 2.5m. If your design includes a bottom drain, we pre-cut and weld a fitting patch into the liner before delivery — you simply connect the drain flange to the prepared aperture on site. Note this requirement in your quote request.
For more on measuring your pond correctly, see our measuring guide. For material selection detail, see choosing the right pond liner material.
“The liner is wonderful quality and fitted like a glove and looks so professional for our koi pond. If you are considering a conventional liner, stop — for the same price you can have a box weld which will look 100% more professional.”
David Coulling — Koi pond, box welded liner
Shapes we manufacture
What to measure
For a koi pond, you need four measurements:
- Length (m) — internal measurement at the longest point
- Width (m) — internal measurement at the widest point
- Depth (m) — from the top of the liner to the base
- Lip allowance (m) — how far the liner should extend over the coping
Not sure what to measure? See our measuring guide.
Frequently asked questions
We recommend our 1.0mm heavy-duty grade for koi ponds. It offers additional resistance to puncture and abrasion from the koi themselves, and gives extra durability at the weld points.
Yes — if your pond design includes a bottom drain, we can pre-cut and weld a fitting patch into the liner. Please mention this when you request your quote.
There is no upper limit on depth. We have manufactured liners for ponds in excess of 2.5m deep. Just provide us with your exact depth measurement.
Yes. Our range of pond liners is inert once installed and safe for fish and aquatic life. It contains no plasticisers or additives that leach into the water.
Ready to get a quote?
Send us your dimensions — we'll reply with a price and a technical drawing the same working day.