A 5,000 LPH pump will rarely deliver 5,000 LPH once it has to lift water and push it through hose, bends and a filter. Choose from the manufacturer’s flow curve at your estimated total head.
The headline flow is normally the pump’s best-case output. Installed flow is the point where the pump curve meets the resistance created by your system.
Start with static head
Measure vertically from the pond’s operating water level to the highest discharge point—not along the hose. A pump returning water 1.2 metres above the pond has 1.2 metres of static head even if the hose is ten metres long.
Maximum head is not an operating point
At maximum head, flow has normally fallen to zero. A pump advertised with a 3m maximum head is not expected to deliver useful water at 3m.
Then allow for friction
Hose walls, connectors, valves, bends, filters and UV units all resist flow. Exact calculation needs component data, but the direction is simple:
- Use the widest sensible hose supported by the pump and filter.
- Keep runs direct and replace clusters of tight elbows with swept bends.
- Allow more margin for long pipe runs, UVs and pressurised filters.
- Clean cages and media before diagnosing a weak pump.
A practical screening example
- Your waterfall lip is 1.0m above the pond surface.
- The hose run is 8m with a filter and several bends.
- Treat 1.0m as static head and add a cautious friction allowance.
- Check the pump curve around that estimated total—not at zero head.
- Reject any candidate that cannot meet the target flow with margin.
Read the pump curve
If the manufacturer provides only maximum flow and maximum head, a linear estimate can screen candidates, but it is not a substitute for a proper curve. Real pump curves are not always linear.