How do filter bacteria change ammonia into less harmful substances in a closed aquarium?

In a closed aquarium, the accumulation of toxic metabolic waste—specifically ammonia—poses a significant threat to aquatic life. To maintain water quality, these systems rely on nitrifying bacteria that reside primarily within the filter material.1

The transformation of ammonia occurs through a two-step process known as nitrification:

• Ammonia to Nitrite: Specific bacteria, such as Nitrosomonas, convert ammonia into nitrite.2
• Nitrite to Nitrate: A second group of bacteria, such as Nitrobacter, then converts the toxic nitrite into nitrate.2

While nitrates are significantly less harmful than ammonia or nitrite, they can still accumulate in a closed system. Because aquarium plants are often insufficient to fully utilize these nitrates, regular partial water changes are typically required to keep nitrate levels low and ensure a healthy environment for the aquarium's inhabitants.1