Understanding the Nitrogen Cycle

The nitrogen cycle, or biological filtration, transforms toxic waste (ammonia) into harmless compounds. Breaking it down:

1. Ammonia (NH₃/NH₄⁺)
   Originates from fish waste, uneaten food, and decaying matter. Even low concentrations (0.02 mg/L) stress fish.

2. Nitrite (NO₂⁻)
   Beneficial bacteria (Nitrosomonas) convert ammonia to nitrite. Nitrite is nearly as toxic as ammonia and must be monitored closely.

3. Nitrate (NO₃⁻)
   A second group of bacteria (Nitrospira and Nitrobacter) convert nitrite to nitrate. Nitrate is far less toxic and can be managed with regular water changes and plants.

4. Plant and Algae Uptake
   Aquatic plants absorb nitrates as fertilizer. In heavily planted setups, nitrate may stay below detectable levels.

By cultivating colonies of these bacteria on your substrate, filter media, and décor surfaces, you build a self-sustaining ecosystem. Never add fish before the cycle completes, or you’ll risk an “ammonia spike” that can decimate your stock.