How to choose the filter for your freshwater aquarium?

The quality of the water in a freshwater aquarium depends largely on the choice and sizing of the filter. A good filtration system not only keeps the water clear and oxygenated, but it also protects your fish and plants from imbalances that can harm their health. This article guides you through the essential criteria and the different types of filters available to help you make the best choice.

1. The importance of the filter in a closed aquarium

1.1. A closed environment with specific needs

In an aquarium, the water is in a closed circuit. Unlike natural environments, the water does not renew itself. This creates several issues:

• Insufficient oxygenation: Without circulation, the water can lack oxygen, which is essential for fish life.
• Waste accumulation: Excrement, food scraps and other suspended particles accumulate, promoting the proliferation of ammonia and nitrites.
• Chemical Imbalances: Without regulation, pH and other water chemistry parameters can fluctuate dangerously.

1.2. The filter's mission

The filter aims to:

• Ventilate and oxygenate the water, generating eddies which promote gas exchange.
• Remove suspended particles and organic debris, preventing the formation of stagnant areas.
• Transform toxic waste (ammonia, nitrites) into nitrates, via the nitrification process carried out by beneficial bacteria, and thus maintain a stable environment for your inhabitants. Find our analysis boxes to measure these parameters precisely.

2. Determine the flow rate and sizing of your filter

The filter flow rate, i.e. the volume of water treated per hour, is a central criterion for the proper filtration of your aquarium. Several factors must be considered:

2.1. Aquarium flora and fauna

• Diversity and number of species: Each species has its own specific oxygen requirements and produces different volumes of waste. For example, a densely populated aquarium or one housing large fish requires a higher flow rate.
• Fish behavior: Active species may stir up more debris, affecting water turbidity. Conversely, calmer fish cause less disturbance.
• Plant Requirements: Some aquatic plants require regular water circulation to access nutrients , while others prefer a more stagnant environment.

2.2. The volume of the aquarium

It is recommended that the filter treats at least 3 to 10 times the total volume of the aquarium per hour. For example, for a 100 litre aquarium, choose a filter with a flow rate of between 300 and 1,000 litres per hour. Be careful: a filter with a capacity lower than the volume of the aquarium exposes your fish to a risk of toxin accumulation.

2.3. Volume and quality of filtration

• Effective filtration volume: A filter with a large compartment can accommodate more filter media (mechanical, biological and chemical), ensuring better water quality.
• Quality of filter media: Quality filter media retain particles and promote the development of nitrifying bacteria . An oversized filter will have the advantage of requiring less maintenance and being more efficient in capturing impurities.

3. The different types of filters for freshwater aquariums

Depending on the configuration of your tank, your aesthetic constraints and the volume of water to be treated, several types of filters are available:

3.1. The internal filter

Features :

• Installation: Placed directly inside the aquarium.
• Advantages: Compact, economical, quiet and easy to install. No risk of external leakage.
• Disadvantages: Reduces living space for fish, appearance sometimes considered unsightly, and limited capacity requiring frequent maintenance.

Directions for use:

• Ideal for aquariums up to 150–200 litres.
• Camouflage it behind decorations or plantations to harmonize your layout.
• Clean it regularly to avoid a drop in flow.

3.2. The external filter

Features :

• Installation: Placed outside the tank, often in a cabinet or under the aquarium.
• Advantages: Large filtration volume, suitable for large aquariums, does not take up space inside the tank and requires less maintenance.
• Disadvantages: More complex installation, risk of leaks if the assembly is not perfect and sometimes noisier.

Directions for use:

• Check for leaks after each maintenance.
• Choose models with low noise levels, especially for aquariums located in living spaces.

3.3. The waterfall filter (or suspended filter)

Features :

• Installation: Suspended on the edge of the aquarium, designed mainly for modest volumes (50 to 100 liters).
• Advantages: Easy to install, space-saving, economical and simple to maintain.
• Disadvantages: Limited flow rate, mainly chosen for its aesthetics, and reserved for aquariums with few people or with low-polluting fish.

3.4. The exhaust filter (or sponge filter)

Features :

• Installation: Consists of an air pump and a filter sponge, often integrated into a plastic tube.
• Advantages: Very economical, gentle flow ideal for small fish and invertebrates, and minimises the risk of aspiration.
• Disadvantages: Less attractive aesthetic appearance, can be noisy due to bubbles, and not suitable for aquariums requiring high flow (usually limited to tanks under 50 litres).

Directions for use:

• Position the tube outlet to attenuate noise.
• Use it in setups where the biotope is delicate (e.g. for small fish or community aquariums).

4. Additional tips for choosing the right filter

• Analyze your real needs: Before purchasing, take stock of the size of your aquarium, the number of inhabitants, and their impact on the water quality.
• Consider the evolution of your tank: If you plan to expand your population or add new species, opt for a filter with a slightly larger capacity.
• Consider maintenance: A larger, more efficient filter may require less cleaning, but accessibility of components for regular maintenance remains an important consideration.
• Consider aesthetics and noise: Especially in living spaces, a quiet filter that is well integrated into the layout contributes to general well-being.

Conclusion

Choosing the right filter for your freshwater aquarium should not be taken lightly. Between flow rate sizing, compatibility with flora and fauna, and the various types of filters available, each criterion contributes to creating a healthy and stable environment for your fish. By taking these recommendations into account and adapting your installation to your specific needs, you will guarantee your aquatic inhabitants optimal water quality and a serene habitat.