You have just filled your aquarium with water. The filter is running, the plants are in place, and the water is becoming clear. However, an essential step is still taking place at a microscopic level: the establishment of biological filtration. It is during this phase that nitrites can accumulate if their production exceeds their transformation.
Understanding the nitrite peak is mainly about better organizing the start-up. You should neither blindly wait for a specific date nor provoke heavy pollution just to obtain a nice curve. The goal is to prepare an aquarium capable of gradually accommodating its population, with consistent analysis results.
Why isn't a new filter immediately mature?
A filter performs several functions. The pump circulates the water. Mechanical elements trap particles. Biological media host micro-organisms that participate in the transformation of nitrogenous waste. These functions do not necessarily become operational at the same rate.
Circulation can work from the very first day while the biological community is still being established. The water appears clean because the particles are removed, but this does not prove a sufficient capacity to process the waste of future fish.
Maturation depends on the environment: available media, temperature, oxygen, water quality, inputs, and potential seeding. Two aquariums started on the same day can therefore evolve differently.
Where does the nitrite peak come from?
Nitrification transforms ammonia compounds into nitrites, and then nitrites into nitrates. At start-up, the different transformation capacities are established gradually. If nitrites are produced faster than they are used, their concentration increases; it may then decrease as the system evolves.
Nitrifiers are not limited to the often-cited names of Nitrosomonas and Nitrobacter. Recent work on freshwater aquariums also shows the role of Nitrospira, some members of which perform complete nitrification, as well as other micro-organisms. For the aquarist, tracking the function remains more accessible than identifying each organism.
How to read a peak curve without turning it into a calendar?
The graph shows a general idea: a concentration can rise, reach a maximum, and then go back down. It does not allow you to predict the day of the peak in your aquarium. Its amplitude and duration vary, and a theoretical curve does not replace your measurements.
A recent study tracked three home aquariums during their installation. The microbial and chemical trajectories were not identical between the tanks. This type of observation serves as a reminder that an average duration does not constitute an individual validation of the start-up.
It is also possible not to observe a marked peak: measurements that are too far apart, low inputs, plant activity, or already colonized media can modify what is seen. In that case, you must examine the protocol and the data, without adding a large amount of waste just to make the NO2 levels rise.
Preparing for the start-up before the fish arrive
Check that the filter is correctly assembled, that the water follows the intended path, and that the media remain bathed in adequate circulation. Prepare the filling water according to its characteristics. For freshwater from the tap, an appropriate conditioner like JBL Biotopol can be used according to its instructions.
Then choose a fishless maturation protocol adapted to the substrate and the installation. A tank with soil that leaches ammonium cannot be monitored exactly like a tank with lightly loaded sand. The inputs necessary for the protocol must be controlled; ammonia-based household products are not suitable for improvisation.
Stocking is prepared in parallel: compatible species, adult size, group needs, and available volume. The end of the biological start-up does not authorize a population that would exceed the physical or behavioral capacities of the tank.
Measurements to follow and what they tell you
| Parameter | Question it helps to answer |
|---|---|
| Ammonium/ammonia | Are the first nitrogenous compounds accumulating? |
| Nitrites, NO2 | Is this intermediate stage detectable or rising? |
| Nitrates, NO3 | How is this form of nitrogen evolving, considering new water and plants? |
| pH and KH | Does the environment remain consistent with the project and biological functioning? |
| Temperature | Are conditions stable and suitable for future inhabitants? |
The JBL ProAquaTest CombiSet Plus NH4 notably includes NH4/NH3, NO2, NO3, pH, and KH. A thermometer completes this monitoring. Follow the instructions and note the units: a nitrate reading cannot be used in place of a nitrite result.
Record the dates, inputs, and water changes. The same value does not have the same meaning before a planned input, just after a dilution, or several days later. Checks must be close enough to understand the evolution; they are often daily during the sensitive phases of a freshwater start-up.
What is the role of Aquipond Aquarium NitriBoost?
Aquipond Aquarium NitriBoost 150 ml is intended to support the biological start-up of the freshwater aquarium. The product sheet indicates, for start-up, 10 ml per 50 liters every two days for two weeks. Check these instructions on your bottle and calculate the quantity based on the actual volume involved.
The frequency of application does not constitute a calendar for introducing fish. The tank's capacity must be checked by analyses and the followed protocol. Similarly, the "up to 750 liters" mention does not necessarily represent a complete start-up treatment for that volume: several applications consume more product than a single dose.
When can the start-up be considered sufficiently advanced?
The decision is based on repeated measurements and the demonstrated capacity to process the protocol's inputs, with ammonium/ammonia and nitrites returned to undetectable levels appropriate for the test. A single zero result obtained in water with almost no load does not provide the same information.
Have your data validated if you are a beginner. Then introduce animals gradually, without suddenly increasing meals. Checks continue after the first introductions: the actual load changes and the filtration must remain capable of handling it.
Actions that can restart an imbalance
Replacing all media, aggressive cleaning, letting the filter media dry out, or stopping circulation for a long time can disturb the community in place. A sudden increase in the number of fish or in feeding can also exceed the available capacity.
Prepare for maintenance to preserve useful media and quickly restore proper functioning. If you change filters, study the transition before removing the old one. Buying a larger device does not immediately give it the biological maturity of the one it replaces.
What if fish are already present during the rise?
The subject then becomes a water quality correction. Check aeration, reduce food intake according to species needs, and prepare an appropriate water change after analyzing the new water. Do not let the animals endure a peak under the pretext that it is a mandatory step.
If fish have difficulty breathing, lose their balance, or if mortality appears, seek veterinary advice immediately. An activator is not a substitute for this care.
To organize your start-up, contact Aquiflor with the volume, substrate, filter, products used, and your analysis table. These elements make it possible to judge the real progress and prepare a suitable population.
Sources
- Study on microbial succession and the start-up of domestic aquarium biofilters.
- McKnight and Neufeld, 2024 — diversity of nitrifying communities.
- OATA — setting up a freshwater aquarium.
- Merck Veterinary Manual — management of start-up problems.
- Aquipond — NitriBoost Aquarium and related Aquishop sheets.
