Nitrite and Nitrate: The Cycle Continues
Deep dive into nitrite and nitrate: Understand \"brown blood disease,\" the long-term effects of high nitrates on fish growth, and the best methods for nutrient export.
Nitrite ($NO_2^-$) and Nitrate ($NO_3^-$)
Once bacteria consume Ammonia, the job isn't done. The Nitrogen Cycle continues through two more critical stages.
Part 1: Nitrite ($NO_2^-$) - The Second Spikes
Nitrite is the byproduct of Ammonia-oxidizing bacteria (Nitrosomonas).
Toxicity
High. While not as instantly aggressive as Ammonia, Nitrite is highly toxic. It binds to the hemoglobin in fish blood, creating methemoglobin, which cannot ferry oxygen. Essentially, the fish suffocates from the inside out, even if the water is full of oxygen.
Symptoms
- Brown Gills: A tell-tale sign of "Brown Blood Disease".
- Gasping: Lack of oxygen availability.
- Rapid Gill Movement.
Treatment
- Water Changes: The only effective immediate removal.
- Salt: Adding a small amount of Aquarium Salt (Chloride ions) can prevent Nitrite from entering the fish's bloodstream. Note: Be careful with plants and scaleless fish.
Part 2: Nitrate ($NO_3^-$) - The End Product
Nitrate is the byproduct of Nitrite-oxidizing bacteria (Nitrospira). It is the final stage of the aerobic nitrogen cycle in most aquariums.
Toxicity
Low. Most fish can tolerate Nitrates up to 40 ppm (parts per million) without issue. Sensitive species (Discus, Shrimp) prefer levels < 20 ppm.
- Short term: High nitrates rarely kill.
- Long term: Chronic high nitrates (>80 ppm) stunts growth, weakens immune systems, and inhibits breeding.
Managing Nitrates
Unlike Ammonia and Nitrite, bacteria do not eat Nitrate effectively in a standard setup (it requires anaerobic conditions). You are the export mechanism.
- The Water Change: The most reliable method. Changing 25% of the water removes 25% of the Nitrates.
- Live Plants: Nature's filter. Fast-growing stem plants and floating plants act as "Nitrate Sponges", consuming it as fertilizer. In heavily planted tanks, you might actually need to add Nitrogen!
- Feeding Control: Less food in = Less Nitrate out.
- Stocking Density: Fewer fish produce less waste.
The Ideal Parameters?
| Parameter | Ideal Level | Action Required if High | | :--- | :--- | :--- | | Ammonia | 0 ppm | Emergency Water Change | | Nitrite | 0 ppm | Emergency Water Change | | Nitrate | 5 - 20 ppm | Routine Maintenance |