Design and Construction
Recommended minimum volume
| Type of fish | Minimum volume |
|---|---|
| Standard Goldfish (1–2 fish) | 500 L |
| Standard Goldfish (various) | 1,000 L (minimum recommended) |
| Small koi (< 30 cm) | 2.000 L |
| Medium-sized koi (30–60 cm) | 5.000 – 10.000 L |
| Large koi (> 60 cm) | 15,000–50,000 L (display tanks) |
⚠️ The most common mistake: ponds that are too small. Adult koi measure 60–90 cm. A single mature koi needs at least 1,000–2,000 L of water.
Depth
- Minimum depth for overwintering: 120 cm — the bottom water does not freeze
- Optimal: 150–200 cm for adult koi
- Shallow zone: Maintain a 40–60 cm zone for marginal plants
Shape and Design
- Flat bottom or slight slope toward the drain: Facilitates cleaning and sludge removal
- Bottom drain: Essential in serious koi ponds—it draws solids toward the filter without the need for manual siphoning
- Deep zone + shallow zone: Koi use the deep zone in summer (coolness) and winter (stable temperature)
- Protection from predators: Birds (herons) are the main problem — taut netting, mesh along the edges, and decorations to prevent access
Materials
| Material | Pros | Cons |
|---|---|---|
| EPDM/PVC Liner (Sheet) | Flexible, moldable, affordable | It can be pierced by sharp roots or rocks |
| Reinforced concrete with a coating | Very durable, any shape | Caro, it needs to be cured and sealed |
| Fiberglass (prefabricated) | Easy installation, clean lines | Limited styles; expensive in large sizes |
| Prefabricated polyethylene tanks | Inexpensive, easy | Available only in small sizes |
Plants for Shade
30–50% of the water's surface area must be shaded in order to:
- Reduce green algae (reduce phytoplankton photosynthesis)
- Normal temperature in summer
- Provide shelter
- Produce O₂ and absorb nitrates