Nitrogen
- Mix with distilled or osmotized water
Ammonia (NH3 / NH4+)
What is it?
Waste products from fish (excreted through the gills and in urine), decomposition of organic matter, and uneaten food. It is the most toxic of the nitrogen-based parameters.
The Two Forms
- NH3 (free ammonia): toxic even at 0.02 ppm
- NH4+ (ammonium ion): much less toxic
- The balance between the two depends on pH and temperature: the higher the pH and temperature, the more free NH3 there is and the greater the danger
Alarm Values
| Level | Situation |
|---|---|
| 0 ppm | Ideal — Mature Aquarium |
| 0.25 ppm | Warning — Aquarium is maturing or overloaded |
| 0.5 ppm | Dangerous |
| >1 ppm | Emergency — Change the water immediately |
Causes of Ammonia Spikes
- Undiscovered dead fish
- Supercharging
- Excess Fish (Overpopulation)
- New, unseasoned aquarium
- Death of the biological filter (following antibiotic treatment or chlorine exposure)
Quick Solution
Change 30–50% of the water + add a water conditioner that temporarily neutralizes ammonia (Seachem Prime is very popular)
Nitrites (NO2-)
What is it?
A product of the oxidation of ammonia by Nitrosomonas bacteria. Highly toxic: it blocks the transport of oxygen in the blood (methemoglobinemia).
Symptoms in Fish
- Rapid breathing on the surface
- Lethargy
- Darker hair color
- Death
Values
| Level | Situation |
|---|---|
| 0 ppm | Ideal |
| 0.1 ppm | Aquarium in the process of cycling |
| >0.3 ppm | Dangerous — water change |
| >1 ppm | Emergency |
Tip: rock salt
In freshwater, adding sodium chloride (sea salt without additives) temporarily reduces the toxicity of nitrites by competing for the gill receptors. It is only a stopgap measure, not a permanent solution.
Nitrates (NO3-)
What is it?
The end product of the nitrogen cycle. Much less toxic than NH3 and NO2, but it accumulates over time and is chronically harmful at high concentrations.