- Confirm TAN with units, pH and temperature.
- Calculate an un-ionized fraction without calling it a safe limit.
- Trace loading, treatment and equipment faults while protecting fish.
01 / Observe the fish and restore failed functions
If fish are gasping, clustering unusually or losing normal behavior, treat the situation as urgent. Check power, air delivery, circulation, water level and temperature immediately. Restore a failed oxygen supply using the tested backup plan, pause feeding during the acute investigation and obtain qualified aquatic-animal-health help when distress continues. Do not wait for a perfect explanation before fixing an obvious stopped air pump.
Ammonia is not reliably diagnosed by smell or water clarity. UF/IFAS emphasizes water testing and explains that feeding and decomposing material contribute to ammonia loading. A clear tank can contain a dangerous concentration, while a cloudy tank can have several different problems. Record what changed before the event: fish additions, feed increase, filter cleaning, water treatment, a power interruption or a new water source.
Reading: Ammonia in Aquatic Systems (FA16) ↗ · Fish Health Management Considerations in Recirculating Aquaculture Systems—Part 3 ↗
02 / Confirm what the test actually measured
Repeat an unexpected result with a fresh sample and the test’s stated procedure. Check reagent expiry, sample volume, reaction time, units and any dilution instructions. Measure pH and temperature from the same water at the same time. Keep the first result in the log rather than replacing it without explanation. An off-scale reading is not a precise concentration.
TAN means total ammonia nitrogen when reported on the nitrogen basis: it combines the nitrogen present in ionized ammonium and un-ionized ammonia. The fraction present in the more toxic un-ionized form increases as pH and temperature rise. Therefore the same TAN result can represent very different exposure conditions. Do not raise pH blindly to correct a separate-looking plant problem while ammonia is elevated.
Reading: Ammonia in Aquatic Systems (FA16) ↗
03 / Work an example without turning it into a target
For a freshwater example, assume TAN is 2.0 mg/L as N and temperature is 20°C. UF/IFAS Table 1 gives an un-ionized fraction of 0.0039 at pH 7.0 and 0.0381 at pH 8.0. Multiplying on the same nitrogen basis gives 0.0078 mg/L NH3-N and 0.0762 mg/L NH3-N respectively. The higher-pH example has roughly 9.8 times the un-ionized ammonia-nitrogen concentration despite identical TAN.
If a comparison specifically requires mass of NH3 rather than NH3-N, multiply by the approximate molecular-mass ratio 17/14. Those example values become approximately 0.0095 and 0.0925 mg/L NH3. Preserve the reporting basis alongside every number. These are calculations from selected source-table inputs, not species-safe limits or instructions to change pH. Salinity, species, exposure and system conditions also matter.
| Freshwater example at 20°C | pH 7.0 | pH 8.0 |
|---|---|---|
| TAN, mg/L as N | 2.0 | 2.0 |
| Source-table fraction | 0.0039 | 0.0381 |
| Calculated NH3-N, mg/L | 0.0078 | 0.0762 |
| Approximate NH3, mg/L | 0.0095 | 0.0925 |
Reading: Ammonia in Aquatic Systems (FA16) ↗
04 / Trace input, conversion and water supply
Check whether the biological filter is actually established and still receiving its intended water and air. Review recent feed and biomass changes against the documented loading plan. Examine captured solids and uneaten feed without stirring accumulated waste into the fish tank. Confirm pH and alkalinity have not moved outside the operating plan, and investigate any medication or disinfectant exposure.
Check the replacement water as well as the recirculating water. NMSU explains that municipal chlorine and chloramine must be removed before that water is used. Do not assume a treatment intended only for chlorine also resolves chloramine, or that a product’s effect on an ammonia test can be ignored. Use the source-water report, treatment instructions and a suitable verification method.
- Record fish behavior, feed, recent additions and system interruptions.
- Verify air delivery, circulation and actual water inventory.
- Confirm TAN, pH, temperature, nitrite and the test reporting basis.
- Inspect the biofilter and solids-handling routine without an uncontrolled waste flush.
- Review source water, treatments, alkalinity and recent maintenance.
- Document the intervention and repeat measurements on a schedule appropriate to the acute problem.
Reading: Important Water Quality Parameters in Aquaponics Systems (CR680) ↗ · Fish Health Management Considerations in Recirculating Aquaculture Systems—Part 3 ↗
05 / Understand the limit of a water-change calculation
For a completely mixed inventory with no new ammonia produced during the calculation, replacing fraction f gives final concentration = starting concentration × (1-f) + replacement concentration × f. Replacing 25% of water containing 2.0 mg/L TAN with water containing zero would calculate to 1.5 mg/L. That is original dilution arithmetic, not a recommended emergency exchange fraction.
Fish continue to produce waste, and water exchanges can alter temperature, pH, gases and other chemistry. If an exchange is part of the established response, use replacement water whose disinfectant removal and compatibility have been verified. Re-test after mixing rather than assuming the calculation describes the living system. Recovery means stable measurements and normal behavior under a controlled loading plan, not one lower test result. Seek diagnosis if problems persist or fish deteriorate.
FIELD QUESTIONTAN fell after a partial water exchange, but the air supply still fails intermittently. Has the cause been fixed?
No. Dilution can lower a measured concentration while the underlying fault remains. Restore and verify the failed function, follow the response plan and keep monitoring the whole nitrogen and oxygen picture.
Parts & buying criteria
Build your own parts & cost worksheet →
Showing aquaponic raft system. 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.
Check size, materials and operating conditions with your chosen supplier before ordering.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.
Check size, materials and operating conditions with your chosen supplier before ordering.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.
Check size, materials and operating conditions with your chosen supplier before ordering.04Raft growing bed1 · illustrated quantity+
Holds plants above water after solids handling and biofiltration. Roots hang below the raft.
Inspect: Compare the depth of this growing section with the shallow channels in the hydroponic lesson.
Maintain: Keep drains accessible and inspect root congestion. Remove crop debris without sending it downstream.
Cleanable bed, supported raft, access to drains and a root-zone aeration plan.
Check size, materials and operating conditions with your chosen supplier before ordering.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.
Check size, materials and operating conditions with your chosen supplier before ordering.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.
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 Florida IFAS ExtensionAmmonia in Aquatic Systems (FA16) ↗
TAN, pH, temperature and fish response.
- University of Florida IFAS ExtensionFish Health Management Considerations in Recirculating Aquaculture Systems—Part 3 ↗
Biosecurity, quarantine, health monitoring and diagnosis.
- New Mexico State University ExtensionImportant Water Quality Parameters in Aquaponics Systems (CR680) ↗
Fish-system water chemistry, oxygen, temperature and nitrification.
The next useful connections.
Fishless cycling: prove the biofilter works
Establish nitrification with a known input and repeated measurements before stocking.
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 →Operation & resilienceFish health, quarantine and daily operation
Prevent avoidable introductions, observe fish before symptoms escalate and keep records useful for diagnosis.
6 min + guided practice →Cycling & water balanceChoosing an aquaponics water-test kit: parameters, units and running costs
Buy measurements you can interpret. Match the test range, reporting basis, calibration and replacement supplies to the questions a fish-and-plant system needs answered.
6 min + guided practice →Cycling & water balanceAquaponics solids filters vs biofilters: choose the function you need
A vessel that catches particles and a surface that supports nitrification solve different problems. Compare their loading assumptions, service access and evidence before buying.
6 min + guided practice →