"Nitrobacter are needed in the aquarium": this phrase often sums up biological filtration. It expresses a valid idea—the essential role of microorganisms—but oversimplifies their identity. A mature filter houses a varied community. For the aquarist, the most useful thing is to understand what this community transforms, where it lives, and how to preserve it.
A new filter does not become biologically operational just because its pump is running. Conversely, a brownish filter is not necessarily faulty. Water measurements and operating conditions provide more reliable indicators than its color.
The filter's task: transforming nitrogenous waste
Fish release nitrogenous compounds. Decomposing food scraps and plant matter also contribute to this load. In an aquarium, nitrification transforms ammonium and ammonia into nitrites, then nitrites into nitrates. These transformations require suitable microorganisms and oxygen.
Nitrites, denoted as NO2, deserve special attention: their presence can put fish in distress. Nitrates, denoted as NO3, correspond to another stage. Filtration that correctly transforms nitrogen may therefore allow nitrates to accumulate. Plants, water changes, and controlling inputs remain necessary depending on the tank's operation.
Why the word Nitrobacter doesn't tell the whole story
Nitrobacter refers to a genus of bacteria capable of oxidizing nitrites. This name is often incorrectly used to designate all filter bacteria. Studies on freshwater aquariums have shown the important role of other groups, notably Nitrospira. Certain members of this latter group can perform complete nitrification: this is known as "comammox."
Archaea, which are microorganisms distinct from bacteria, also participate in the oxidation of ammonia. A study published in 2024 highlighted the importance of Nitrospira comammox in the freshwater biofilters studied. This does not allow for identifying the species present in your filter based on a photo, an odor, or a nitrite test.
The practical consequence is simple: aim to maintain functional biological filtration. Buying a product because a text promises "Nitrobacter" is not enough to demonstrate its precise composition or its effectiveness in your setup.
Where do useful microorganisms live?
They colonize surfaces: sponges, porous media, substrate, decor, and other areas bathed by water. The filter offers them a location where water, the compounds to be transformed, and oxygen circulate. A large part of this activity is associated with biofilms attached to the media.
This is why retrieving only water from an old aquarium is not the same as transferring a mature filter. Likewise, performing a partial water change with properly prepared water does not suddenly remove the entire community from the tank. The complete replacement of colonized media represents a very different intervention.
Conditions that help the filter function
| Point to monitor | What to observe | Useful action |
|---|---|---|
| Circulation | Weakened output, clogged intake, kinked hose | Check water flow and clogging |
| Oxygenation | Still surface, aeration failure, fish in distress | Restore gas exchange and investigate the cause |
| Organic load | Food scraps, decaying leaves, increased population | Remove accessible waste and review feeding |
| Stability | pH variation, harsh maintenance, recent treatment | Measure water and adapt the intervention |
pH and alkalinity also influence biological function. A KH value recommended for a pond should not be imposed on all aquariums: species needs differ. Any correction must take into account measurements and the population. Adding minerals "for bacteria" without a diagnosis can create another imbalance.
Cleaning sponges without starting from scratch
Useful maintenance restores circulation without trying to make every surface sterile. When the media need to be rinsed, use water removed from the aquarium and proceed gently. Keep elements moist during the intervention and reassemble the filter according to its manual.
Do not replace all reusable media at the same time. Truly exhausted or damaged consumables may require replacement, but this should be prepared while considering their function. Mechanical foam, carbon used after a treatment, and permanent biological media are not managed the same way.
Prepare the bucket, parts, and tools before stopping the device. You will reduce the time spent looking for a seal while the filter is open. Upon restarting, check priming, seals, and output; an audible pump does not prove that water is circulating correctly through the media.
How to know if biological filtration is sufficient?
Measure ammonium/ammonia and nitrites, then track their trend. In an established aquarium adapted to its population, one aims for the absence of nitrites detectable with an appropriate test. However, an isolated reading does not describe the whole situation: note the date, feeding, any water change, and recent interventions.
The JBL ProAquaTest CombiSet Plus NH4 notably combines NH4/NH3, NO2, and NO3 measurements, as well as pH and KH. Check the reading limits, units, and expiration dates of reagents. The color of a tube photographed under yellow light can be misleading: read the test under the conditions specified in its manual.
What is the role of bottled bacteria?
An activator can accompany a startup or a restart when its instructions match the situation. JBL Denitrol is presented as an activator containing aquarium bacteria and enzymes. Its commercial presentation does not constitute a microbiological analysis of your filter.
Follow the dosage, storage conditions, and any compatibility instructions for the bottle used. Do not add multiple activators in the hope of multiplying the maturation speed. No addition can permanently compensate for a stopped filter, lack of oxygen, or excessive feeding.
New water conditioning still fulfills another function. A product like JBL Biotopol prepares tap water according to its manual; it does not replace biological media or water testing.
Three situations that require more vigilance
A new aquarium: the time passed is not enough to validate maturation. Organize the startup without exposing fish to deliberate pollution, then verify the system's capacity before gradual stocking.
A replaced filter: prepare the transition to keep part of the filtration already operational, when the equipment and sanitary state allow. Then monitor the values; a new, more powerful device does not immediately possess the maturity of the old one.
A breakdown or treatment: the duration of the shutdown, oxygenation, and product used can change the risk. Do not assume everything has returned to normal as soon as the motor restarts. In the presence of nitrites or fish in distress, restore aeration, measure the water, and promptly ask for professional advice.
To take stock of your filter, send its model, the tank volume, the fish present, and the latest analysis results to Aquiflor. This information allows for choosing between targeted maintenance, adjusting the setup, or assistance with a startup.
Sources
- McKnight and Neufeld, 2024 — study of nitrifying communities in aquarium biofilters.
- Study on bacteria related to Nitrospira associated with nitrite oxidation in freshwater aquariums.
- OATA — setting up and looking after an aquarium.
- JBL — Denitrol presentation and Aquishop product sheets linked in the article.
