Best Bio Filter Media for Freshwater, Planted & Reef Tanks in 2022

The truth about bacteria and biological filtration

A lot of old information still circulates among aquarists and the internet concerning the bacteria that perform biological filtration. Current research about nitrifying bacteria has replaced most of the traditional thinking about nitrification in aquariums but “fish lore” lives on for decades on the internet.

Let’s look at some of the new facts about nitrifying bacteria through a Question and Answer session.

Nitrifying bacteria will die if there is not enough oxygen.

False. Nitrifying bacteria remain alive and active even in low oxygen conditions. This is how they survive in nature, where oxygen levels rise and fall every day.

The biological filter in an aquarium needs lots of oxygen and aeration to help the bacteria get rid of ammonia and nitrite.

False. Normal water movement and aeration provides enough oxygen for the biological filter. Excessive aeration is unnecessary.

Saltwater aquariums contain different bacteria than freshwater tanks

Mostly true. Some species of nitrifying bacteria are found only in fresh or saltwater. But there are some nitrifying bacteria that live equally well in both types of aquariums.

Nitrifying bacteria live only solid surfaces like biological filter media.

False. Nitrifying bacteria live in the water but also form colonies on solid surfaces in the aquarium.

Denitrifying bacteria require low oxygen conditions to remove nitrate.

True. Their biochemistry functions best in a low-oxygen environment. However, some species, under the right conditions, will denitrify in oxygenated water.

More surface area means more biological filtration.

False. The number of bacteria in the biofilter is dependent on the level of ammonia load in the aquarium. The biological filter only grows to the level of ammonia produced in the aquarium. Biofilter material simply add extra protected growing area, supplementing the natural “bio spaces” inside the aquarium.

The truth is nitrifying bacteria will grow on just about any surface they can in your aquarium.

The “biological filter” is not in one place, like a power filter. It is spread out in the water, on the glass, gravel, live rock, plants and biological filter media.

If this is true, why do we need biofilter media? We’ll cover that next!