Clear Water Made Simple: How to Choose the Correct Pond Pump & Filter
A garden pond is a beautiful addition to any Kiwi backyard, but keeping it healthy requires the right "heart" and "lungs"—your pump and filter. If you've ever felt overwhelmed by flow rates and head heights, this step-by-step guide is for you.
Follow these four simple steps to find the perfect match for your pond.
Step 1: Calculate Your Pond Volume
Before you shop, you need to know exactly how much water you are moving.
For Rectangular Ponds: Length (m) x Width (m) x Average Depth (m) x 1000 = Total Litres
For Circular Ponds: 0.8 x Diameter (m) x Diameter (m) x Depth (m) x 1000 = Total Litres
The Golden Rule: For a healthy ecosystem, aim to circulate the entire volume of your pond once every 1 to 2 hours.
Step 2: Account for Your "Fish Load"
Fish produce waste, which means your filter has to work harder to keep the water safe.
Decorative Pond (No Fish): You can circulate the water once every 2 hours.
Goldfish Pond: Aim to circulate the water once every hour.
Koi Pond: Koi are heavy waste producers. You should choose a pump and filter rated for double your actual pond volume.
Step 3: Understand "Head Height"
This is where many people get tripped up. A pump rated for 3,000 Litres Per Hour (LPH) will move less water the higher it has to lift it.
Vertical Lift: Measure the distance from the surface of the water to the highest point the water reaches (e.g., the top of a waterfall).
Friction Loss: Long hoses and sharp bends slow water down.
Pro Tip: Always choose a pump slightly more powerful than your "bare minimum" to account for this resistance.
Step 4: Choose the Right Filter Type
A good filter provides both mechanical (removing debris) and biological (breaking down toxins) filtration.
All-in-One Submersible Filters: Perfect for small ponds or wine barrels. The pump and filter are a single unit that sits inside the pond.
Pressure Filters: Ideal for medium ponds and waterfalls. Because they are pressurized, water can be pushed uphill after leaving the filter.
Gravity/Flow-Through Filters: Best for large ponds or heavy fish loads. These sit at the highest point, and water flows back into the pond via gravity.
Quick Selection Sheet
| Pond Type | Total Water Volume | Recommended Pump Flow | Recommended Filter |
| Small Water Feature | Up to 500L | 1,000 LPH | All-in-One Submersible |
| Small Fish Pond | 1,000L | 1,500 – 2,000 LPH | 2,500L Pressure Filter |
| Medium Garden Pond | 3,000L | 4,000 – 5,000 LPH | 6,000L Pressure Filter |
| Large Goldfish Pond | 5,000L | 7,500 – 10,000 LPH | 10,000L Flow-Through |
| Koi Pond (High Waste) | 10,000L+ | 15,000 – 20,000 LPH | Heavy Duty UV System |
Summary Checklist
Find your litres: (L x W x D x 1000).
Double the requirement: If you have Koi or many goldfish.
Check the "Head Height": Ensure the pump can reach your waterfall's height.
Add a UV Clarifier: Essential if your pond gets a lot of NZ sun to prevent "green water."