Why NFT flow consistency matters
Nutrient Film Technique relies on a stable, shallow stream that wets roots and preserves oxygen exposure. When per-channel flow drifts, film depth changes fast because channel area is small. Low flow can create dry zones, while high flow can reduce aeration and increase waste.
Flow, velocity, and residence time
Velocity is computed from per-channel flow divided by wetted area (A = w × d). Residence time is channel length divided by velocity and shows contact duration. Use these outputs to keep nutrients moving without shocking roots. If residence time becomes excessive, refresh rates and temperature control can suffer.
Slope-based capacity checks
Slope affects how easily a thin film travels along the channel. The calculator compares your plan to a Manning-style capacity estimate using slope, roughness, and geometry. If measured flow exceeds the estimate, expect depth to rise and oxygen exposure to drop. If flow is far below capacity, velocity may be too low and solids can accumulate.
Example data and interpretation
Example: 6 channels, 6.0 L/min total, 100 mm width, 2.0 mm depth, 6.0 m length, 1.5% slope, 20 C. Per-channel flow is 1.0 L/min and area is 0.0002 m2. Velocity is about 0.083 m/s and residence time about 72 seconds. This sits near a practical lower boundary for settling control.
| Scenario | Channels | Total Flow (L/min) | Width (mm) | Depth (mm) | Length (m) | Slope (%) |
|---|---|---|---|---|---|---|
| Leafy greens | 6 | 6.0 | 100 | 2.0 | 6.0 | 1.5 |
| Warm day boost | 6 | 7.2 | 100 | 2.2 | 6.0 | 1.8 |
| Compact rack | 4 | 3.2 | 90 | 1.8 | 4.5 | 1.2 |
Operational tuning checklist
Split total flow evenly, then verify each channel with a timed jug test. Confirm slope with a level and measure inlet-to-outlet drop for long runs. Recheck after cleaning because roots and biofilm change resistance. Log your preferred settings using the CSV export for repeatable adjustments.