Biological filtration is the foundation of aquarium chemistry - the nitrogen cycle in action. Two distinct bacteria genera handle the work: Nitrosomonas oxidizes ammonia (NH3) to nitrite (NO2). Nitrospira oxidizes nitrite to nitrate (NO3). These colonies live primarily on biological media (ceramic rings, bio-balls, K1, sintered glass) and live rock. Surface area drives capacity - that's why "1 liter of bio-media per 100 liters of water" is the rule of thumb. Bacteria die from: chlorine, antibiotics that target gram-negatives (Maracyn 2 less so), 24h+ without ammonia source, drying out. Bacteria thrive on: consistent ammonia source, steady oxygen, neutral pH, 75-82°F.
Reviewed by the Fast Aquatics husbandry team · Updated May 2026
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