About Ammonia

Any time organic matter is introduced to an aquarium — including fish, invertebrates, live plants, or live rock — ammonia will be produced. Ammonia is the primary waste compound in any aquarium and the starting point of the nitrogen cycle, the biological process by which beneficial bacteria convert harmful waste into less harmful compounds. Understanding and managing ammonia is the foundation of a healthy tank.

Ammonia and the nitrogen cycle

When setting up a new tank, it is normal to see ammonia levels rise during the cycling period — the initial weeks when beneficial bacteria are establishing themselves in the filter. Rather than relying on ammonia-removing products, which only address ammonia already present in the water and can’t affect future ammonia that fish continuously produce, adding nitrifying bacteria is a more effective long-term approach. Nitrifying bacteria establish a biological filter that converts ammonia on an ongoing basis. Once that filter is established, it will continuously convert ammonia on its own, keeping levels in check.

Why ammonia is dangerous

Ammonia is acutely toxic to fish and invertebrates, and lethal levels can accumulate rapidly in the absence of healthy, established beneficial bacteria. Making things more complicated, ammonia’s toxicity isn’t fixed — it shifts depending on the pH and temperature of your water.

Ammonia exists in two forms: unionized ammonia (NH₃) and ionized ammonia (NH₄⁺, also called ammonium). NH₃ is the more toxic of the two — it passes through fish tissue more easily and causes damage at lower concentrations. NH₄⁺ is less toxic but still harmful at elevated levels. The balance between the two shifts with pH: as pH rises, more ammonia converts to the toxic NH₃ form. For example, an ammonia reading that is tolerable at a pH of 7.8 could be lethal at a pH of 8.4. Higher water temperatures also push the balance toward the more toxic NH₃ form, compounding the risk.

The practical takeaway: the same ammonia reading can mean very different things depending on your pH and temperature. In saltwater tanks with naturally higher pH, this is especially worth keeping in mind.

When ammonia becomes a problem

Ammonia is expected during a new tank cycle, but it can also spike in established tanks when maintenance lapses. Skipping water changes, a dirty filter, an overcrowded tank, or the use of certain medications that disrupt the biological filter can all cause ammonia to rise. Any fish death or illness should prompt an immediate ammonia test.

Testing and target levels

Ammonia is measured in parts per million (ppm). The target is always 0 ppm — any detectable amount should be taken seriously. Test regularly as part of your monthly routine, and immediately any time fish appear stressed or a death occurs.

Signs of ammonia stress in fish

• Rapid gill movement
• Clamped fins
• Bacterial infections
• Mortality

Corrective actions

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In all cases of elevated ammonia levels, after completing the steps below, add an ammonia remover like Fritz Rescue A.C.C.R. or Fritz Complete to treat ammonia currently present, then add nitrifying bacteria (FritzZyme® 7 for freshwater or FritzZyme® 9 for saltwater) to fortify your biofilter.

• 0.5–1 ppm — Reduce feeding, clean the filter, and siphon the substrate to remove excess debris
• 2–3 ppm — Stop feeding temporarily and perform a 25% water change. Clean the filter and siphon the substrate
• 4–5 ppm — Perform a 50% water change and follow the steps above. Consult your local aquarium dealer to help identify and correct the underlying cause
• 6–7 ppm — Perform a 75% water change, follow the steps above, and consult your local aquarium dealer right away