What do ammonia, nitrite and nitrate numbers mean?
Evidence review: August 10, 2026
A number is not interpretable until its substance and reporting basis are known. Total ammonia nitrogen, unionized ammonia, ammonium, nitrite and nitrate are not interchangeable. A result reported as nitrogen is also numerically different from the same species reported as the whole ion.
The short version: copy the exact analyte, unit and reporting basis from the method. Record pH and temperature with an ammonia result. Verify an unexpected result before assigning a cause, but begin low-risk system protection at once when animals are in danger. No result on this page is a universal safe concentration.
A nitrogen result has seven parts
| Part | Example | Why it matters |
|---|---|---|
| Substance | Total ammonia, NH3, NH4+, NO2- or NO3- | They are different chemical claims |
| Reporting basis | As N or as the whole species | The same sample gives different numbers |
| Unit | mg/L as N | ppm is not enough when the basis is missing |
| Method | Product, lot, range and procedure | Methods differ in what they measure and resolve |
| Sample | Tank, replacement water or opened bag | Results from different water are not one time series |
| Context | Time, pH and temperature | Ammonia equilibrium and exposure change with conditions |
| Uncertainty | First nonzero step, blank and repeat | A colour block is not an exact zero |
Translate a reporting basis
This calculator changes only the reporting basis for the same species. It does not convert ammonia into nitrite or nitrate. It also does not convert total ammonia into NH3, because that requires pH and temperature.
Exact factors used: NH3-N to NH3, 17.031 / 14.007; NO2-N to NO2-, 46.0055 / 14.007; NO3-N to NO3-, 62.0049 / 14.007. Reverse conversions divide by the same factor. Always retain the original result.
Estimate the unionized fraction of freshwater TAN
A total ammonia test measures or estimates NH3 plus NH4+. In freshwater, their equilibrium changes with pH and temperature. This calculator applies the Emerson equation reproduced by the U.S. EPA. The entered concentration must already be total ammonia nitrogen in mg/L as N.
Limits: this is a freshwater equilibrium estimate, not a direct NH3 measurement or a Neocaridina safety calculator. Input error in TAN, pH or temperature carries into the estimate. Ionic composition can also matter. Keep the measured TAN, pH, temperature, method and calculation together.
What the direct Neocaridina experiment tested
Melo's 2023 doctoral study ran separate 96-hour acute tests on juvenile N. davidi. Each definitive test used a control plus five concentrations, ten juveniles per vessel and two vessels per treatment. Animals were fasted, water was fully renewed daily, and the vessels had continuous aeration. Mean treatment conditions were about pH 7.70 to 7.73, 25.2 to 25.5 C and dissolved oxygen 5.71 to 5.99 mg/L.1
The vessel is the shared exposure unit. Ten animals in one vessel are not ten independent water replicates, and two vessels per treatment is limited treatment replication. The nominal controls were not analytical zeros: the ammonia control averaged 0.85 mg/L N-TAN and the nitrite control averaged 0.12 mg/L NO2-N in the reported water tables. This is a doctoral thesis chapter; this review did not locate a separately published journal article for the experiment.
| 96-hour estimate | Study result | 95 percent interval |
|---|---|---|
| Total ammonia nitrogen | 19.98 mg/L N-TAN | 15.77 to 25.31 |
| Unionized ammonia as nitrogen | 0.48 mg/L NH3-N | 0.38 to 0.60 |
| Nitrite as nitrogen | 0.69 mg/L NO2-N | 0.60 to 0.80 |
These are median lethal concentration estimates, not concentrations at which nothing happened. The study also reported gill changes across exposed groups. Its one-tenth arithmetic safety factors were not separately tested chronic-safe concentrations. The experiment does not establish a harmless detectable level, a breeding threshold, a transport limit or a home-aquarium target.
Reporting basis changes the apparent number. The study's 0.69 mg/L NO2-N is about 2.27 mg/L NO2- when expressed as the whole nitrite ion. Its 0.48 mg/L NH3-N is about 0.584 mg/L molecular NH3. Neither conversion changes the exposure. It only prevents comparison of unlike labels.
Nitrate still has a direct evidence gap
This review found no controlled chronic nitrate-only experiment in N. davidi. Results from marine or brackish shrimp, fish, drinking-water limits and short mixed-nitrogen tests cannot supply a species-specific chronic aquarium threshold. Molt & Moss keeps nitrate below 20 mg/L on the operation's registered reporting basis as a conservative house action level. It is not a demonstrated toxicity boundary or proof that a lower reading is complete water quality.
Investigate a nitrogen event without guessing
- Protect the system. Restore failed air or filter flow, stop the identified input and prepare known replacement water. Do not wait for a perfect diagnosis when several animals cannot right themselves.
- Preserve the original label. Photograph the method scale or instrument screen and record analyte, basis, unit, range, product, lot and expiry.
- Repeat intelligently. Use a fresh sample, correct timing and a blank or reference when available. Dilute only when the method provides a validated procedure.
- Measure context. Record pH, temperature, dissolved oxygen when available, filter output, recent feeding, deaths, maintenance, power loss and new additions.
- Measure the replacement water. A change cannot dilute an analyte below the replacement concentration by mixing alone.
- Make one documented intervention. Calculate and record actual replaced volume, restore equipment, then sample after adequate mixing.
- Follow the animals and the numbers. Record balance, righting, distribution, feeding response, molts and mortality. Sequence does not prove the nitrogen result caused every sign.
Do not add salt as a universal nitrite antidote for freshwater Neocaridina, or assume a conditioner makes a measured result biologically harmless. No direct experiment located here validates either response for the exact species, chemistry, concentration and duration. If the tank cannot be controlled, move animals only to a separately commissioned system with known water.
What the evidence does not prove
- That
0 ppmmeans the substance is absent below the method's resolution - That any detectable result has the same biological meaning at every pH and temperature
- That nitrate presence proves a tank can process the intended load
- That a 96-hour LC50 is a chronic safe level or a treatment trigger
- That an animal's movement diagnoses ammonia, nitrite or nitrate
- That surviving one excursion proves no gill injury or later effect
- That a water conditioner, plant, resin or bottled culture clears an event without measurement
- That 20 mg/L nitrate is a validated Neocaridina toxicity boundary
Primary sources and measurement authorities
- Melo, 2023. Efeito de compostos nitrogenados no camarão Neocaridina davidi e na rã Aquarana catesbeiana. Doctoral thesis, Federal University of Minas Gerais. Direct juvenile acute exposures, mortality estimates and gill histology.
- U.S. Environmental Protection Agency, 2013. Freshwater Aquatic Life Ambient Water Quality Criteria for Ammonia. Freshwater NH3 and NH4+ equilibrium and the Emerson equation. The criteria themselves are not Neocaridina-specific aquarium limits.
- U.S. Environmental Protection Agency. Nutrients. Nitrogen analytes, reporting bases and analytical-method distinctions.
- U.S. Environmental Protection Agency. Effluent Monitoring Procedures: Nutrients. NO2-N and NO3-N formula-mass conversions.
- Holroyd et al., 2026. An ecophysiological approach to improving health outcomes of ornamental shrimp during aquarium trade and transportation. Transport-specific evidence gaps.
Build a defensible water-test record.
Commission the complete aquarium system.