Best Bio Filter Media for Freshwater, Planted & Reef Tanks

There are hundreds of kinds of aquatic micro-organisms living in our aquariums. They filter out debris, break down organic substances and recycle nutrients.

When we discuss aquarium biological filtration we are mainly concerned with the “removal” of ammonia (NH₃) and nitrite (NO₂^-). The process is a biochemical transformation of harmful ammonia to nitrite and then nitrite to nitrate (NO₃^-).

This two-step transformation is achieved through two types of bacteria. The first type of bacteria convert ammonia to nitrite, which is also toxic to aquatic life.

A second type of bacteria convert nitrite to relatively harmless nitrate. The bacteria use these substances as an energy source. The transformation of toxic ammonia and nitrite to nitrate is a byproduct of the bacteria’s metabolism.

These bacteria are called “nitrifying” bacteria because the process of converting ammonia to nitrate is called “nitrification”.

A third type of bacteria convert nitrate to into nitrogen gas. This bacteria-driven process is called denitrification. Denitrification and reducing nitrate levels is especially important to reef aquarists who keep corals.

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!

As we’ve discussed bacteria will find their “home” throughout your aquarium. They’ll spread out everywhere, reproduce and form colonies.

Imagine if you tried to build a house on a rocky coast that was constantly buffeted by abrasive waves. What if your neighborhood was periodically demolished by a mudslide?

How about if a tornado flipped your home once a month?

Doesn’t sound like a nice location to settle down, does it? It’s the same for the bacteria in the aquarium.

Gravel cleaning, glass scraping, washing plastic plants, water changes and anything else that disturbs the bacterial balance can reduce the effectiveness of the “biological filter” inside the aquarium.

Biofilter media are intended to provide a safe and stable environment for the bacteria, no matter what happens in the rest of the aquarium.

The bacteria colonies living in and on the biofilter media act as a nitrifying bacteria farm, releasing a steady supply of new beneficial bacteria to recolonize the entire aquarium.

Most types of biofilter material redirect the water flow to pass through a bed or chamber of media.

Suspended organic matter, uneaten fish food and solid fish waste will settle in the biofilter media because of the slower water velocity in the bed of biological media.

The heavier particles will settle in and on top of the biofilter media. For example, if you load your canister filter so incoming water first passes through the bio media, the media will act as a coarse mechanical filter and collect sludge and debris.

The accumulated organics tend to stimulate the growth of fast-growing non-nitrifying bacteria. These bacteria grow very quickly and can crowd out the beneficial nitrifying bacteria.

The best location for biofilter media is in the cleanest part of the filter system.

Use prefilter media like sponge pads to remove solids before the water flows through the bio media. You can rinse or replace the prefilter media and leave the bacteria on the biofilter media undisturbed.

Not every manufacturer provides instructions on how much to use per gallon. This may be because biofilter media is often pre-packaged for a specific filter.

The truth is there is no exact scientific formula for aquarium biofiltration media calculation.

Every aquarium is different in regards to fish and invertebrate size, number and amount of food added by the aquarist.

Nitrate reduction is similar. If a manufacturer recommends a certain use rate, try that first. More media can be added later if necessary.