- Locate solids removal and nitrification in each design before sizing the plant area.
- Size a bed or raft from the published depths and volume ratios, with their conditions attached.
- Decide when a separate plant loop repays its extra equipment and management.
01 / Where the two treatment jobs happen
In a media bed the aggregate does both jobs: SRAC 5007 says the media supports roots and can act as a biofilter and solids filter, and SRAC 454 reports gravel serving as the sole biofilter in some systems. SRAC 454 also gives the failure mode: media tends to clog, and an overloaded gravel bed can produce ammonia from decaying organic matter rather than remove it.
A raft treats less in the plant zone but still nitrifies: SRAC 454 says raft hydroponics provides sufficient nitrification if solids are removed from the flow before it reaches the trough, so a clarifier comes first; SRAC 5007’s small-scale layout also runs the effluent through a biofilter tank it sizes, like the clarifier, at 15–20 percent of fish tank volume. NMSU CR680 notes that raft and media systems sometimes omit a separate biofilter, but most still use one. NMSU Guide H-173 describes a decoupled system as two independent recirculating units joined by a one-way valve to a hydroponic reservoir; because the fish side is a recirculating aquaculture system (RAS), its solids removal and nitrification stay on that loop.
| Criterion | Media bed | Raft | Decoupled |
|---|---|---|---|
| Solids removal | In the aggregate; clogging is the failure mode (SRAC 454) | Separate clarifier before the trough (SRAC 454) | Inside the fish RAS; H-173 notes the discharged solids can be re-mineralized |
| Nitrification | On the media (SRAC 5007) | Trough walls and raft undersides once solids are removed (SRAC 454); SRAC 5007 adds a biofilter tank | Inside the fish RAS; the plant loop is dosed (H-173) |
| Crops that fit | Wide range; awkward for short crops (HLA-6721) | Leafy greens; narrower range (HLA-6721) | Any hydroponic crop; recipe tailored (H-173) |
| Published depth | 12–14 in (HLA-6721); 6–12 in (SRAC 5007) | 10–12 in, 6 in often works (SRAC 5007) | Set by the hydroponic method |
| Sizing rule | 1:1 or 2:1 bed to tank (HLA-6721); 1 ft³ tank to 2 ft³ gravel (SRAC 454) | 60–100 g feed per m² per day (SRAC 454) | Plant side is dosed, not fed |
| Pump stops | Rapid wilting (SRAC 454) | Plant water supply unaffected (SRAC 454) | Each loop fails alone (H-173) |
Reading: Aquaponics—Integrating Fish and Plant Culture (SRAC 454) ↗ · Principles of Small-Scale Aquaponics (SRAC 5007) ↗ · Important Water Quality Parameters in Aquaponics Systems (CR680) ↗ · Decoupled Aquaponics: A Comparison to Single-loop Aquaponics (Guide H-173) ↗
02 / Plant sites and the crops each suits
OSU HLA-6721 says media beds act like pots, so the watering pattern rather than the bed limits the crop; their weakness is short crops such as lettuce, where cleaning media off roots is time-consuming. Rafts make quick crops easy to pull and trim, but HLA-6721 says they grow a more limited range.
SRAC 454 gives green leaf lettuce at 48 plants per 8 by 4 ft raft sheet (16 per m²) on a four-week cycle; SRAC 5007 says an 8-inch spacing works for most leafy greens. Those are the cited crops, not a universal density. H-173 adds that single-loop effluent may not reach the concentrations fruiting crops need, which a decoupled plant loop can dose for.
Reading: Aquaponics (HLA-6721) ↗ · Aquaponics—Integrating Fish and Plant Culture (SRAC 454) ↗ · Principles of Small-Scale Aquaponics (SRAC 5007) ↗ · Decoupled Aquaponics: A Comparison to Single-loop Aquaponics (Guide H-173) ↗
03 / Depth and volume as the sources print them
HLA-6721 says media beds function better at 12–14 inches deep and that a 1:1 or 2:1 bed-to-tank volume ratio is generally used, warning that its simplest tank-to-bed layout drops the fish level if two beds fill at once. The media-bed chapter carries the same figures with its commissioning steps.
SRAC 454 recommends 1 ft³ of rearing tank per 2 ft³ of 1/8–1/4 inch pea gravel for flood-and-drain systems, with conditions: tilapia to 0.5 lb per gallon, no solids removed, beds cultivated between crops and inoculated with red worms. For rafts it gives 1 foot of water and 60–100 g feed per m² per day. Because about 75 percent of a raft system’s water sits in the troughs, SRAC 454 suggests gravel and NFT run at roughly 25 percent of the raft feeding ratio.
Reading: Aquaponics (HLA-6721) ↗ · Principles of Small-Scale Aquaponics (SRAC 5007) ↗ · Aquaponics—Integrating Fish and Plant Culture (SRAC 454) ↗
04 / Service, oxygen and the moment the pump stops
SRAC 454 lists the media bed’s burdens: weight needing strong support, clogging by solids, microbial growth and roots left after harvest, anaerobic zones, and gravel that is hard to move or clean. OSU HLA-6729’s maintenance table, credited to a producer checklist, puts clearing roots from bed drains on the weekly list and cleaning the biofilter, clarifier and filters on the monthly list. Rafts trade that for exposed roots: SRAC 454 names fry, ostracods and snails, and UVI runs a diffuser every 4 feet for 6–7 mg/L oxygen; SRAC 5007 asks for an air stone per 10 square feet and rafts washed but never dried, since nitrifying microbes colonize them.
When the pump stops, SRAC 454 says drained gravel holds very little water and wilts rapidly, while a raft plant’s water supply is unaffected. Fish need air either way: HLA-6721 says to consider putting aeration on a separate or backup power supply, and HLA-6729’s troubleshooting table suggests pouring sump water into the fish tank every 1–2 hours until power returns. H-173 counts losing one loop without harming the other among the reasons to decouple.
Reading: Aquaponics—Integrating Fish and Plant Culture (SRAC 454) ↗ · Principles of Small-Scale Aquaponics (SRAC 5007) ↗ · Nitrification and Maintenance in Media Bed Aquaponics ↗ · Aquaponics (HLA-6721) ↗ · Decoupled Aquaponics: A Comparison to Single-loop Aquaponics (Guide H-173) ↗
05 / Cost drivers and when decoupling pays
The sources give direction, not prices. SRAC 5007 calls media beds easy and inexpensive to set up and DWC more management-intensive and costly for a beginning grower. SRAC 454 counts eliminating a separate biofilter among the main advantages of aquaponics, notes the sturdy structure gravel needs, calls commercial raft troughs expensive, and declines to generalize economics because costs vary by location.
H-173 says decoupled systems need greater capital, space, expertise and management, and that hydroponic nutrient salts must be added to the plant tank to make up for the missing nutrient build-up; it concludes single-loop is probably easier and more economical for small, hobby and leafy-crop systems. Decoupling pays when one of its listed problems is yours: cold-water fish with warm crops, a fruiting crop needing a tailored recipe, a plant side that must be disinfected for an audit, or a loop you must shut down for treatment.
Reading: Principles of Small-Scale Aquaponics (SRAC 5007) ↗ · Aquaponics—Integrating Fish and Plant Culture (SRAC 454) ↗ · Decoupled Aquaponics: A Comparison to Single-loop Aquaponics (Guide H-173) ↗
06 / Decide, then size
The treatment decision fixes what you must buy before the plant area is set. The exercise applies the published ratios to a 300-gallon tank, the size SRAC 5007 calls average for small systems; it is arithmetic, not a fish-load recommendation.
- List the year’s crops: mostly short-cycle greens points to raft; a mixed or tall list to a media bed; fruiting crops needing a recipe, or cold-water fish with warm crops, to decoupling.
- Decide where solids leave. No clarifier means a media bed at SRAC 454’s ratio with its conditions; a clarifier opens the raft option.
- Size the plant side by the matching rule: HLA-6721’s 1:1 or 2:1 or SRAC 454’s 1:2 for beds; 60–100 g/m²/day for rafts.
- Check gravel weight for a bed, or the three quarters of system water sitting in raft troughs.
- Write the outage response before buying: a bed needs flow back quickly, a raft holds its water, a decoupled pair needs one plan per loop.
- Decouple only if a reason from section 05 applies.
FIELD QUESTIONYou have a 300-gallon fish tank and want a flood-and-drain media bed. What bed do the published ratios suggest, and how much daily feed would the same footprint support as a raft?
300 gallons is 300 ÷ 7.48 ≈ 40 ft³. SRAC 454’s 1:2 rule gives 80 ft³ of gravel, 80 ft² at 12 inches deep, about two and a half 4 × 8 ft beds; two beds give 64 ft³ (1:1.6), three give 96 ft³ (1:2.4). HLA-6721’s 1:1 gives 40 ft³, about 40 ft² at 12 inches or 34 ft² at 14; its 2:1 lands on the same 80 ft³. As raft, 80 ft² is 80 ÷ 10.76 ≈ 7.4 m², and SRAC 454’s 60–100 g/m²/day gives roughly 445–745 g of feed per day. None of this sets a fish count: SRAC 454 ties its gravel ratio to a tilapia density with no solids removal, and feed comes from the fish you hold.
Reading: Aquaponics (HLA-6721) ↗ · Aquaponics—Integrating Fish and Plant Culture (SRAC 454) ↗ · Principles of Small-Scale Aquaponics (SRAC 5007) ↗
Parts & buying criteria
Showing aquaponic media bed. Quantities describe the teaching model. Specify real working volume, support, fittings and instruments for your installation.
01Fish tank1 · illustrated quantity+
Houses fish and receives the pumped return. Feed is an input to this living system.
Inspect: The fish are generic silhouettes, with no species or stocking-rate recommendation. Cutaway reveals the tank interior.
Maintain: Observe behavior and feeding response; keep a record of water tests and changes.
Smooth accessible tank, secure cover and species-appropriate volume determined by an aquaculture design.
Supplier links can be added by the publisher. The criteria stand independently.02Solids separator1 · illustrated quantity+
Intercepts settleable waste before it accumulates in later treatment and growing components.
Inspect: Open the front of the vessel. Brown particles beneath the central baffle represent collected waste, not a settling simulation.
Maintain: Inspect accumulation and remove it on an observation-based schedule without flushing it into the growing bed.
Accessible waste drain, removable internals and a design matched to expected solids and flow.
Supplier links can be added by the publisher. The criteria stand independently.03Biological filter1 · illustrated quantity+
Provides wetted surface for nitrifying organisms. This teaching layout shows a separate biofilter.
Inspect: The blue carriers indicate surface area; cyan flow does not measure nitrification or oxygen availability.
Maintain: Protect the established community during service. Verify nitrogen readings before and after changing loading or equipment.
Media and aeration matched to the intended feed load, water conditions and an independently reviewed design.
Supplier links can be added by the publisher. The criteria stand independently.04Aggregate growing bed1 · illustrated quantity+
Supports plants in aggregate with a controlled drain; this layout retains upstream solids treatment and biofiltration.
Inspect: Cutaway reveals aggregate, planted roots and a screened drain. The water level is illustrative.
Maintain: Observe wetting, drain clearance and accumulated solids; preserve biological function through staged maintenance.
Fish-compatible aggregate, verified saturated support load and accessible drain guard.
Supplier links can be added by the publisher. The criteria stand independently.05Sump & return pump1 · illustrated quantity+
Collects gravity drainage and pumps water to the fish tank, closing this particular circuit.
Inspect: This is the lowest collection point. The tank, filters and bed have progressively lower illustrative water levels.
Maintain: Check sump level, intake and leaks. Test whether drainage can be contained when power stops.
Usable reserve volume, pump service access, level protection and verified delivery at the required head.
Supplier links can be added by the publisher. The criteria stand independently.06Air supply1 · illustrated quantity+
A separate air pump supplies diffusers to the fish tank, biofilter and growing bed.
Inspect: White bubbles indicate air delivery only; bubble count is not a dissolved-oxygen reading.
Maintain: Check air lines, diffusers and backup arrangements. Verify oxygen with suitable measurement.
Airflow at operating depth, compatible diffusers and resilience reviewed for the living load.
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.
- Southern Regional Aquaculture Center · hosted by OSU ExtensionPrinciples of Small-Scale Aquaponics (SRAC 5007) ↗
Design, media-bed depth, biofilter sizing and aeration, potassium/calcium/iron supplementation and the UVI feed-to-area rule restated in ounces per square foot; applicability depends on system.
- New Mexico State University ExtensionImportant Water Quality Parameters in Aquaponics Systems (CR680) ↗
Fish-system water chemistry, oxygen, temperature and nitrification.
- New Mexico State University ExtensionDecoupled Aquaponics: A Comparison to Single-loop Aquaponics (Guide H-173) ↗
Two independent recirculating units joined by a one-way valve to a hydroponic reservoir; listed benefits (tailored recipes, cold-water fish with warm crops, disinfection, shutting down one loop); greater capital, space, expertise and management, supplemental nutrient salts, and the conclusion that single-loop suits small, hobby and leafy-crop systems.
- Oklahoma State University ExtensionAquaponics (HLA-6721) ↗
Coupled fish, microbes and plant needs.
- Oklahoma State University ExtensionNitrification and Maintenance in Media Bed Aquaponics ↗
Biofilter establishment, nitrogen testing and maintenance.
The next useful connections.
Media-bed aquaponics: grow without hiding the waste
Design an accessible aggregate bed, verify flood and drain behavior and preserve its biological function.
6 min + guided practice →System designsRaft, NFT and decoupled aquaponics
Compare the plant side of the system while keeping fish treatment requirements visible.
6 min + guided practice →Cycling & water balanceSolids removal and biological filtration
Separate particle collection from dissolved nitrogen conversion and design maintenance access into both.
6 min + guided practice →Operation & resilienceOxygen and outage resilience
Measure oxygen where it matters and rehearse a recovery plan before fish depend on it.
6 min + guided practice →