- Calculate gross volume and measure actual inventory.
- Draw gravity elevations and service access.
- Verify minimum level and maximum drain-back.
01 / Working volume is a measured inventory
For a rectangular vessel, internal length × width × actual water depth in metres × 1,000 gives gross water volume in litres. A 1.2 m × 0.6 m tank at 0.25 m depth has a gross volume of 180 L before displacement. External dimensions and nominal capacity are not the same as actual water inventory.
Plants, media, equipment and pipes displace or hold water. Calibrate level marks by measured filling when precision matters. Include connected tanks, filters, beds and plumbing in chemical concentration calculations.
| Inventory location | When it changes | Design consequence |
|---|---|---|
| Reservoir / sump | Pumping, refill and drain-back | Low-level pump reserve and high-level freeboard. |
| Flood tray | Every irrigation event | Peak moving volume and overflow route. |
| Channels and pipes | Shutdown and restart | Water that returns after power loss. |
| Media pore water | Wetting and drainage | Measured loading differs from an empty vessel. |
02 / Draw elevations, not just connections
Gravity flow requires an appropriate difference in water surface or pipe elevation and sufficient capacity along the entire route. A pipe can connect two vessels physically while failing to drain at the intended rate. Avoid high points that trap air and low pockets that retain debris.
Place unions, strainers and drains where they can be reached with mature plants in place. Keep walkways, harvest access and equipment replacement space in the layout. Full water and media loads require suitable supports and structural review for the installation.
Reading: Aquaponics—Integrating Fish and Plant Culture (SRAC 454) ↗
03 / Test the extreme states
Mark the lowest safe pump level during maximum delivery and the highest reservoir level after all possible drain-back. Test with the real media and containers. Coordinate several flood zones so their combined worst case is understood.
An overflow needs a safe destination. Discharging onto a floor or into an electrical area simply moves the failure. A sensor is useful but should not be the only protection against an undersized drain.
- Measure internal dimensions and calibrate the working-volume marks.
- Run normal operation and record all vessel levels.
- Stop power and observe the complete drain-back until levels stop changing.
- Restart and confirm pumps remain primed and branches recover.
- Test foreseeable control faults with plain water before plants or fish are loaded.
- Label operating marks, shutoffs and the overflow destination.
04 / Recheck after each expansion
Adding channels increases both delivery demand and retained water; adding media changes displacement and total mass. A larger pump may require a larger return. Do not treat expansion as only an inlet-plumbing change.
Keep the circuit drawing and water inventory with the nutrient and maintenance records. The person mixing the next batch needs the current volume, not the volume from the first construction sketch.
FIELD QUESTIONWhy can a reservoir overflow only when power fails?
Water held in elevated beds and plumbing returns when pumping stops. A tank sized only for normal running inventory lacks drain-back freeboard.
Parts & buying criteria
Showing ebb and flow. Quantities describe the teaching model. Specify real working volume, support, fittings and instruments for your installation.
01Nutrient reservoir1 · illustrated quantity+
Stores the measured nutrient solution beneath or beside the growing area.
Inspect: Compare the surface with the pump intake or lower roots; freeboard is deliberate.
Maintain: Record level before refilling, keep light out and verify temperature, EC and pH.
Opaque, cleanable, intended-use container with volume marks and service access.
Supplier links can be added by the publisher. The criteria stand independently.02Pump & supply1 · illustrated quantity+
Moves nutrient solution from the reservoir to the growing area.
Inspect: Trace installed lift and branching; the pump label does not prove delivered flow.
Maintain: Measure output after service and inspect intake, filter and minimum water level.
Pump curve matched to installed head, required pressure and service needs.
Supplier links can be added by the publisher. The criteria stand independently.03Growing tray1 · illustrated quantity+
Contains supported media pots above the lower reservoir.
Inspect: Inspect the flood level, pot bases and accessible drain position.
Maintain: Verify full drainage and inspect moisture in representative pots.
Rigid cleanable tray with independent overflow and adequate support.
Supplier links can be added by the publisher. The criteria stand independently.04Root-zone mediumFor illustrated containers · illustrated quantity+
Stores moisture and air around the roots in the illustrated containers.
Inspect: Compare the medium surface with irrigation and drainage.
Maintain: Inspect wetting at several depths; prevent fines from reaching drains and emitters.
Prepared, stable grade matched to the irrigation method and crop.
Supplier links can be added by the publisher. The criteria stand independently.05Drain & overflow1 · illustrated quantity+
Returns drainage to the reservoir and provides a controlled high-water route.
Inspect: Follow the full slope and look for the separate high-level opening.
Maintain: Test pump-off drain-back and keep roots and medium out of the outlet.
Accessible fittings and verified capacity under normal and fault conditions.
Supplier links can be added by the publisher. The criteria stand independently.Evidence beside the lesson.
Source checks: September 2026. The geometry, inspection exercises and worksheets are original teaching material. The named organizations have not endorsed or reviewed this site.
Published recipe rates and planning ranges retain their source context. Calculator equations are accounting tools; they do not predict uptake, yield, toxicity or safe stocking. Model dimensions, water speeds, roots and fish counts are illustrative. Verify species, crop, source water and product labels for a real system.
- Southern Regional Aquaculture Center · hosted by OSU ExtensionAquaponics—Integrating Fish and Plant Culture (SRAC 454) ↗
Tank-to-treatment-to-growing-to-sump layout and production tradeoffs.
The next useful connections.
Ebb and flow: flood, drain, observe
Build a flood table, size its working water inventory and tune irrigation from the medium’s actual wetting and drying.
6 min + guided practice →Equipment & layoutPumps, head and delivered flow
Choose a pump from its operating curve and verify every branch under real installation conditions.
Interactive tool · 6 min + guided practice →