- Locate exposed nutrient solution throughout a system.
- Separate algae appearance from a flow or oxygen problem.
- Plan repairs and cleaning without inventing a live-system chemical dose.
01 / Start with exposed wet surfaces
A functioning hydroponic system supplies water and nutrients. When light reaches that solution or wet growing surfaces, algae can establish. UNH recommends excluding light and cleaning between crops. Follow the green film upstream and downstream rather than assuming the main reservoir is the only source.
Opaque covers are a useful first control, but inspect their fit and suitability. Do not seal air passages that the design needs or block overflow, inspection access and ventilation. A cover that excludes light while preventing a drain check creates a different maintenance problem.
Reading: Hydroponics at Home ↗
02 / Check function as well as appearance
Oklahoma State describes algae obstructing irrigation equipment and attracting nuisance insects, with oxygen consumption during decomposition of dying mats. A thin visible film and a blocked intake are different operating situations. Record the location, extent and effect on delivery before choosing the response.
Check actual flow through each branch, look for restricted screens and inspect root access. Do not rely on the pump’s sound or the return from one channel. Algae control is not a reason to stop needed aeration or let NFT roots dry during a lengthy inspection.
Reading: Algae Control for Greenhouse Production ↗ · Small-scale hydroponics ↗
03 / Trace a complete light-leak route
Use this inspection route as a practical checklist. Look during the normal lighting period and include translucent fittings, open plant holes and edges that became exposed after a transplant or harvest. Photograph repeat locations so you can see whether the same gap reopens.
| Location | Look for | Practical correction |
|---|---|---|
| Reservoir | Translucent walls, lifted lid and open service ports | Use a suitable opaque cover while preserving access and required airflow |
| NFT channels | Unoccupied holes, translucent end caps and return fittings | Close unused holes and shade compatible wet components |
| DWC surface | Gaps around rafts or lids | Fit light-excluding pieces without restricting the system |
| Feed and return tubing | Clear lengths exposed to lamps or sun | Use suitable opaque tubing or an accessible external shade |
| Plug and media surfaces | Continuously wet, illuminated areas | Review irrigation and support; do not dry out seedlings |
| Bench and floor | Leaks and nutrient spills | Repair the leak and remove standing water |
Reading: Hydro hints: Deep water culture ↗ · Cornell Controlled Environment Agriculture Hydroponic Lettuce Handbook (2013) ↗
04 / Make an operating repair safely
If a pump or intake needs hands-on service, isolate electrical equipment as its instructions require and provide an appropriate temporary delivery plan for living plants. Keep the interruption brief and verify function after reassembly. Route cables and water according to the equipment and electrical installation requirements.
Remove accessible debris without pushing it into roots or the recirculating return. Preserve the system’s intended aeration and circulation, but recognize that moving water can still grow algae. Aeration supports roots; it is not a substitute for light exclusion and hygiene.
Feed to the crop program rather than starving the crop to suppress algae. Verify EC and the batch record before changing concentration. A rising EC with falling volume is a useful observation, but it does not establish the exact ion balance or automatically specify a top-up dose.
- Identify and record the exposed wet locations and any restricted delivery.
- Restore essential flow and aeration, using the equipment’s safe service procedure.
- Close light leaks with materials suited to the system and preserve inspection access.
- Repair leaks and remove spills around the system.
- Recheck actual flow after the repair and review the nutrient record.
- Inspect the same points on the next daily round and schedule accessible deep cleaning between crops.
Reading: Small-scale hydroponics ↗ · Electrical Conductivity and pH Guide for Hydroponics ↗ · Algae Control for Greenhouse Production ↗
05 / Clean first, then disinfect empty equipment
Between crops, remove residues and physically clean serviceable tanks, channels, screens and pump components. Follow material compatibility guidance. Cleaning removes deposits; disinfection is a subsequent step with a suitable labeled product, the specified contact time and any required rinsing.
Do not carry a greenhouse surface-disinfectant concentration into a living nutrient reservoir. This guide specifies no hydrogen peroxide, copper or algaecide dose around roots, and none for fish-connected water. If algae remain disruptive despite light exclusion and maintenance, seek system-specific advice before introducing a treatment.
Reading: Clean and disinfect the greenhouse ↗ · Hydroponics at Home ↗
06 / Worked case: a covered tank, a green return
A reservoir has a fitted opaque lid, but a clear return pipe and three empty basket holes show green growth. The remaining crop looks healthy and return flow is still adequate. The inspection has identified exposed locations, not proof of a fertilizer shortage or plant infection.
Shade or replace the compatible clear section, close unused holes and confirm the return remains accessible. Record the spots and monitor flow; remove accessible debris using the operating procedure and schedule full cleaning between crops. If growth interferes with delivery, address that fault promptly instead of waiting for harvest.
FIELD QUESTIONShould you increase fertilizer strength to make the crop outcompete the algae?
No. Follow the crop’s nutrient program, fix light exposure and operating faults, and verify measurements. A stronger solution can create plant stress and does not resolve the exposed wet surface.
Reading: Small-scale hydroponics ↗ · Algae Control for Greenhouse Production ↗
Parts & buying criteria
Build your own parts & cost worksheet →
Showing nutrient film technique. Quantities describe the teaching model. Specify real working volume, support, fittings and instruments for your installation.
01Reservoir1 · illustrated quantity+
Holds the recirculating nutrient solution. This is the common sampling and refill point for both channels.
Inspect: In cutaway view, compare the water surface with the pump intake. The drawing leaves room above the water; it does not specify a working volume.
Maintain: Record the level before adding water. Inspect the cover, clean accessible deposits and keep the intake submerged during use.
Opaque, cleanable container rated by its manufacturer for the intended use; accessible lid and drain.
Check size, materials and operating conditions with your chosen supplier before ordering.02Pump & supply1 · illustrated quantity+
Lifts solution from the reservoir to the channel inlets. Cyan packets indicate the direction of delivery.
Inspect: Follow the rising supply pipe and its branch to each channel. Both inlets need an observable supply.
Maintain: Disconnect power before opening the pump. Inspect its inlet screen and confirm both branches flow after reassembly.
Compare the pump curve at the installed lift and pipe resistance; include service access and replacement availability. Supply the pump, timer and any air pump through ground-fault protection (GFCI/RCD), keep plugs and cord connections above the water line with a drip loop, and switch off and unplug before reaching into the solution.
Check size, materials and operating conditions with your chosen supplier before ordering.03Growing channels1 · illustrated quantity+
Contain the shallow stream beneath the plants and guide it toward the return.
Inspect: Open the cutaway to find the channel floor beneath the roots. The slope is exaggerated for reading.
Maintain: Look along each channel for ponding, debris or an obstructing root mat; inspect the outlet before changing the pump.
Removable covers, supported slope, smooth cleanable surfaces and outlets accessible with plants in place.
Check size, materials and operating conditions with your chosen supplier before ordering.04Plant baskets6 illustrated · illustrated quantity+
Bridge the opening in the channel cover while allowing roots to pass through.
Inspect: In exploded view, the baskets lift above the channels. The open slats reveal the relationship between support and roots.
Maintain: Check that each rim sits securely and that roots are not pinched at transplanting or inspection.
Match the basket rim and hole diameter; allow removal without damaging adjacent plants.
Check size, materials and operating conditions with your chosen supplier before ordering.05Support mediumFor 6 baskets · illustrated quantity+
The illustrated expanded clay supports the seedling in its basket. The channels are not filled with aggregate.
Inspect: Select the brown pebbles and separate the basket in exploded view. Media texture is simplified.
Maintain: Remove loose particles before installation. Inspect whether the starter plug stays appropriately moist.
Select a stable grade that stays in the basket; compare water retention, dust and cleaning requirements.
Check size, materials and operating conditions with your chosen supplier before ordering.06Gravity return1 · illustrated quantity+
Collects channel outflow and brings it back to the reservoir without a second pump.
Inspect: Trace the low ends of both channels into the common return. Inspect the full path before assuming the circuit is clear.
Maintain: Remove obstructions and check for leaks. Test drainage with the pump off during commissioning.
Removable unions, supported pipe and sufficient drain capacity under the actual installation conditions.
Check size, materials and operating conditions with your chosen supplier before ordering.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.
- University of New Hampshire ExtensionHydroponics at Home ↗
Algae conditions, light exclusion, aeration and cleaning between crops.
- Oklahoma State University ExtensionAlgae Control for Greenhouse Production ↗
Algae effects, light exclusion and prevention. Chemical treatment tables are not reproduced.
- University of Minnesota ExtensionSmall-scale hydroponics ↗
Root support, transplanting, light, aeration and cleaning.
- Oregon State University ExtensionHydro hints: Deep water culture ↗
Aerated water culture layout and operation.
- Cornell University CEA Program (M. Brechner and A. J. Both)Cornell Controlled Environment Agriculture Hydroponic Lettuce Handbook (2013) ↗
Pond-stage lighting: supplemental 100–200 µmol/m²/s at plant level for a total of 17 mol/m²/d of natural plus supplemental light; the 17 mol/m²/d target having to be matched with downward airflow to prevent tip burn, and the statement that without that airflow the authors were not able to go over 12 mol/m²/d, with the caveat that the data are for cultivar Ostinata only.
- Oklahoma State University ExtensionElectrical Conductivity and pH Guide for Hydroponics ↗
Water analysis, salinity, pH and monitoring.
- NSW Department of Primary IndustriesClean and disinfect the greenhouse ↗
Physical cleaning followed by appropriate disinfection.
The next useful connections.
From reservoir to roots.
Follow a nutrient film system from its first inlet to its last root. Learn what each part does, what to inspect, and how the pieces work together.
12 min + model exploration →Growing methodsDeep water culture: build an aerated root bath
A complete single-vessel DWC workflow, from water level and air delivery to nutrient management and harvest.
6 min + guided practice →Nutrients & mixingReservoir management and solution replacement
Use a water-and-nutrient ledger to distinguish top-ups, rebalancing and a complete batch change.
Interactive tool · 6 min + guided practice →Build, operate & troubleshootCommissioning and daily care
Turn assembled equipment into a repeatable operating system, with a first-crop checklist and a useful log.
6 min + guided practice →Build, operate & troubleshootTroubleshooting and sanitation
Trace symptoms to measurable causes, contain a problem and clean the system without creating another one.
6 min + guided practice →