Do Molly Fish Need A Filter? (With Recommendations)

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Arranging a molly fish tank raises many questions, including what equipment these beautiful creatures actually need.

One question I often receive is whether molly fish require a filter. In this article, I will answer this question, and walk you through the entire process of picking the right one for your tank.

Let’s dive in.

Do Molly Fish Need A Filter?

Yes, molly fish do require a filter in their aquarium.

The presence of a filter helps maintain a stable and healthy environment for these fish by eliminating waste products, excess food, and potential toxins.

Filters also play a key role in oxygenating the water, an essential factor for the overall well-being of the molly fish.

Here is what you should know:

  • Water Quality: Molly fish require clean and stable water conditions. Filters help maintain this by removing waste, leftover food, and potentially harmful chemicals that can affect the health of the molly fish.
  • Oxygenation: Filters not only clean the water but also oxygenate it by causing surface agitation. Molly fish, like other aquatic species, require well-oxygenated water to breathe and thrive.
  • Bacterial Balance: In an aquarium, beneficial bacteria help in the breakdown of waste into less harmful substances. Filters provide a suitable surface for these bacteria to grow, indirectly benefiting the molly fish by keeping the water clean.
  • Stress Reduction: Molly fish can become stressed in dirty water, leading to a weakened immune system and increased susceptibility to diseases. By maintaining water cleanliness, filters help reduce stress levels for molly fish.
  • Longevity: With proper filtration leading to better water conditions, molly fish can live longer, healthier lives. The average lifespan of a well-cared-for molly fish can range from three to five years.

Also Read: Molly Fish Tank Setup

Advantages Of Using A Filter In Your Molly Fish Tank

If you are still not convinced, here are the main purposes of having a filter in a molly fish tank:

1. Enhances Water Circulation

A filter in a molly fish tank promotes consistent water circulation, which is crucial for the well-being of the fish.

Water circulation ensures equal distribution of heat and nutrients, and also prevents stagnation.

This consistent circulation plays a vital role in creating an optimal living environment for molly fish.

Consider this:

  • Heat Distribution: Consistent water circulation due to a filter ensures that heat from a tank heater is evenly distributed throughout the tank. This is critical for molly fish that need a stable temperature for optimal health.
  • Nutrient Distribution: With good water circulation, essential nutrients are evenly distributed, making it easier for molly fish to feed and stay nourished.
  • Prevention of Stagnation: Water filters prevent the water from becoming stagnant, which is important because stagnant water can breed harmful bacteria and parasites that could threaten the health of molly fish.

2. Decreases The Need For Frequent Water Changes

A high-quality filter is crucial in managing water conditions, thereby limiting the frequency of water changes required.

Regular water changes, while essential, can cause stress to molly fish.

By minimizing the necessity for frequent water changes, a filter fosters a more stable environment that helps to alleviate stress in molly fish.

Consider the following benefits:

  • Consistency: Water parameters can fluctuate significantly with regular water changes, potentially stressing molly fish. A filter aids in maintaining these parameters consistently, contributing to a stable tank environment.
  • Stress Minimization: Each water change introduces a potential stressor for molly fish. By reducing the need for frequent water changes, a filter significantly decreases this source of stress.
  • Time Efficiency: Incorporating a filter in your molly fish tank not only contributes to better health for your fish but also saves time by decreasing the frequency of labor-intensive water changes.

3. Removes Ammonia, Nitrites, And Nitrates

The main purpose of a filter is to eliminate ammonia, nitrites, and nitrates.

These compounds are toxic to molly fish and can accumulate quickly in an aquarium, especially in overstocked tanks.

Consider the following:

  • Toxin Removal: Filters house beneficial bacteria that convert toxic ammonia and nitrite into less harmful nitrates, thereby protecting molly fish from these harmful toxins.
  • Prevention of Illness: High levels of ammonia, nitrite, and nitrate can cause a variety of illnesses in molly fish. A filter helps prevent these health problems.
  • Supports Higher Stocking Levels: A well-functioning filter allows for higher stocking levels in the tank by effectively removing harmful toxins, providing more flexibility for molly fish enthusiasts.

Which Filter Type Is Ideal for Molly Fish?

Unfortunately, there is no universal filter that suits all molly fish tanks.

Nonetheless, canister filters are strongly advised for larger tanks, whereas power filters are more suitable for smaller tanks.

Here is a concise overview of the available filter options:

1. Canister Filters

Canister filters are renowned for their robustness and versatility, effectively executing mechanical, chemical, and biological filtration tasks.

They are especially well-suited for larger aquariums housing molly fish, thanks to their high filtration capacity and ability to be tailored to the specific requirements of these fish.

Here’s what you need to know:

  • Enhanced Filtration Capacity: Canister filters can efficiently handle substantial water volumes, making them highly suitable for accommodating larger molly fish tanks.
  • Versatile Filtration Capability: These filters can accommodate a variety of media, enabling effective mechanical, chemical, and biological filtration, which is crucial for maintaining the health of molly fish.
  • Customizable Options: Canister filters can be customized to match specific filtration needs, allowing for precise adjustments in creating an optimal environment for molly fish.

2. Power Filters

Power filters, also known as hang-on-back filters, are an excellent choice for molly fish tanks of small to medium sizes due to their user-friendly design and efficient filtration capabilities. 

These filters are easy to install, require minimal maintenance, and are particularly suitable for novice molly fish enthusiasts.

Consider the following key features:

  • User-friendly Design: Power filters are specifically designed for ease of use, simplifying the setup and maintenance process. This aspect is particularly advantageous for beginners who are new to molly fish keeping.
  • Effective Filtration: Despite their straightforward design, power filters provide comprehensive mechanical, chemical, and biological filtration, contributing significantly to the well-being of molly fish.
  • Optimized for Smaller Tanks: Power filters offer an adequate filtration capacity for molly fish tanks of small to medium sizes, making them a suitable option for such setups.

3. Internal Filters

These filters are placed inside the aquarium and are a good choice for smaller tanks housing molly fish. They are compact, silent, and provide a decent level of filtration.

Here is what you should know about internal filters:

  • Compact and Quiet: Internal filters have a small footprint and operate silently, causing minimal disturbance to molly fish.
  • Decent Filtration: While not as powerful as canister or power filters, internal filters provide sufficient filtration for smaller molly fish tanks.
  • Ease of Installation: Internal filters are easy to install, which can be advantageous for those new to keeping molly fish.

4. Undergravel Filters

Undergravel filters are placed under the substrate of the aquarium and pull water through the gravel, providing biological filtration.

While not as efficient as the other types, they can be used in conjunction with other filters in a molly fish tank.

Here is what to keep in mind:

  • Unobtrusive: Undergravel filters are hidden from view, maintaining the aesthetic appeal of the molly fish tank.
  • Supplemental Filtration: While not ideal as a standalone filter, they can supplement other filters to enhance the biological filtration beneficial to molly fish.
  • Ease of Use: These filters are simple to operate, offering a user-friendly option for molly fish keepers.

Key Factors To Keep In Mind When Selecting A Filter For Your Molly Fish

When selecting a filter for your molly fish, you need to consider several key factors.

These include the size of your tank, the number of fish you plan to keep, and the specific filtration needs of molly fish.

You also need to consider the maintenance requirements of the filter and your personal experience and comfort in managing the filtration system:

  • Tank Size: The size of your molly fish tank will greatly influence the type and capacity of filter you need. For instance, larger tanks often require canister filters due to their high filtration capacity.
  • Fish Load: The number of molly fish in your tank, also referred to as fish load, directly impacts the level of filtration needed. More molly fish mean more waste, which necessitates a filter with a higher capacity.
  • Filtration Needs: Molly fish require clean, well-oxygenated water for optimal health. Therefore, a filter that offers mechanical, chemical, and biological filtration is necessary for a molly fish tank.
  • Maintenance Requirement: Different filters come with different maintenance requirements. It’s important to choose a filter you are comfortable maintaining to ensure the health of your molly fish.
  • Experience Level: Some filters require a higher level of expertise to set up and operate. Make sure to choose a filter that matches your experience level in keeping molly fish.

When it comes to molly fish, my pick would be the Fluval C4 Power Filter (link to Amazon):

Temporary Measures When A Filtration System Is Unavailable

If you don’t have a filter in your molly fish tank, there are a few things you can do in the meanwhile:

1. Prevent Overcrowding In Your Aquarium

If a filtration system is unavailable, preventing overcrowding in your aquarium becomes vital. 

Overcrowding increases waste production and can lead to toxin buildup that’s harmful for molly fish.

Keeping a lower number of fish helps maintain a healthier and less stressful environment:

  • Lower Waste Production: Fewer molly fish in the tank means less waste produced, reducing the risk of harmful toxin buildup.
  • Reduced Stress: Overcrowding can cause stress among molly fish. Keeping fewer fish helps maintain a calmer environment, promoting better health.
  • Optimized Oxygen Availability: A lesser number of fish means less competition for the available oxygen, especially crucial in the absence of a filter to aerate the water.

Also Read: Do Molly Fish Need A Bubbler?

2. Enhance The Frequency Of Water Changes

Without a filter, enhancing the frequency of water changes can help maintain water quality and the overall health of your molly fish.

Regular water changes help to reduce the concentration of harmful substances and replenish essential minerals.

Here is what you should know:

  • Toxin Dilution: Regular water changes help dilute harmful substances such as ammonia, nitrites, and nitrates, thus creating a healthier environment for molly fish.
  • Stabilized Parameters: Water changes can help stabilize water parameters like pH, temperature, and hardness, which are essential for the well-being of molly fish.
  • Mineral Replenishment: Fresh water brings in essential minerals necessary for the health of molly fish.

To monitor the water quality, I personally use the API Master Test Kit (link to Amazon).

3. Employ Ammonia Neutralizers

Ammonia neutralizers can be used temporarily when a filtration system is unavailable.

These neutralizers can detoxify ammonia, one of the most harmful substances for molly fish, thus making the water safer.

Keep this in mind:

  • Toxin Reduction: Ammonia neutralizers can convert toxic ammonia into a non-toxic form, reducing the risk to molly fish.
  • Immediate Effect: These neutralizers work quickly, offering immediate protection to molly fish in a filter-less tank.
  • Ease of Use: Ammonia neutralizers are simple to use, making them a convenient temporary solution for molly fish keepers.

4. Introduce An Abundance Of Aquatic Plants

Aquatic plants can absorb some of the toxins present in the water and produce oxygen.

This can be particularly helpful in a filter-less tank where toxin levels can build up quickly, posing a risk to molly fish:

  • Natural Filtration: Aquatic plants can absorb harmful substances like nitrates, effectively acting as a natural filter and making the environment safer for molly fish.
  • Oxygen Production: Plants produce oxygen, which is especially beneficial in the absence of a filter to aerate the water for molly fish.
  • Stress Reduction: Aquatic plants can also provide shelter and reduce stress among molly fish.

Also Read: 11 Plants Your Molly Fish Will Love In Their Tank


If you are in a rush, here is a brief summary of what I discussed earlier:

  • Filters are vital in molly fish aquariums as they aid in creating a stable and clean environment by removing waste, surplus food, and potential toxins. They contribute significantly to water oxygenation, a factor critical for molly fish health.
  • Moreover, filters facilitate efficient water circulation, ensuring uniform distribution of heat and nutrients, and averting water stagnation. This, in turn, helps cultivate an optimal habitat for molly fish.
  • Filters also promote the growth of beneficial bacteria, integral to the breakdown of waste and maintaining water cleanliness, which indirectly benefits molly fish health.
  • Finally, the use of a filter decreases the frequency of water changes, reducing stress for molly fish. It efficiently removes harmful compounds like ammonia, nitrites, and nitrates, and enables a higher stocking density in the tank.