What is Biological Filtration?
Biological filtration relies on colonies of beneficial bacteria that live on filter media, substrate, and surfaces in the aquarium. These bacteria process toxic nitrogen compounds produced by fish and waste.
How it works
- Ammonia (NH₃/NH₄⁺) → converted by Nitrosomonas bacteria → Nitrite (NO₂⁻)
- Nitrite → converted by Nitrobacter bacteria → Nitrate (NO₃⁻)
This conversion is essential for fish survival and a stable nitrogen cycle.
Common biological filtration media
- Ceramic rings
- Bio-balls
- Porous sponges
- Live plants (contribute to bacterial colonization)
Importance
A fully functional biological filter prevents ammonia and nitrite spikes and is critical during aquarium cycling and for long-term water stability.