Molly Fish Tank Setup: A Comprehensive Beginner’s Guide

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You can’t just throw your molly fish to a brand new tank without preparations – they simply won’t survive. There are a few things to consider beforehand.

In this article, I will take you step-by-step and explain how to set up a molly fish tank from scratch.

You will learn how to choose the right equipment, adjust the water, pick the right tank mates, and a lot more.

So, without further ado, let’s get started. Here is a quick overview of what I’m about to discuss:

Minimum Tank Size20 gallons
Ideal Tank Size30+ gallons
Temperature72°F – 78°F
pH Level7.5 – 8.5
Ammonia Level0 ppm
Nitrite Level0 ppm
Nitrate Level< 20 ppm
Water Hardness10-30 dGH

Also Read: Molly Fish Care Guide

Tank Size

Molly fish thrive best in a spacious tank that provides ample room for swimming and exploration, with a minimum recommended size of 20 gallons and an ideal size of 30 gallons or more.

This recommendation aligns with the molly fish’s active nature and the need to mimic its natural habitat as closely as possible.

Let’s delve into the key reasons behind this suggestion:

  • Spacious Environment: Molly fish are active swimmers and need space to move around freely. A larger tank of at least 30 gallons provides this, mimicking their natural spacious habitats.
  • Stress Reduction: Overcrowding can lead to stress and disease in molly fish. A larger tank helps prevent this, promoting healthier, happier fish.
  • Water Quality: Larger tanks tend to maintain more stable water parameters. This stability is crucial as molly fish prefer consistent water temperature and pH levels.
  • Population Control: Molly fish breed prolifically. A bigger tank of 30 gallons or more allows for population expansion, reducing the risk of overcrowding.
  • Decoration and Planting Space: Molly fish appreciate a well-decorated environment with plants. A larger tank offers enough space for decorations without impeding their swimming area.

Also Read: Molly Fish Tank Size

Water Parameters

When setting up a molly fish tank, the most important parameters to consider are the temperature, pH, hardness, and nitrogenous compounds:

  • pH Level: Molly fish require slightly alkaline water. The optimal pH range is between 7.5 and 8.5, which helps maintain their body functions efficiently.
  • Ammonia: The level of ammonia in the tank should always be 0 ppm (parts per million). Ammonia is toxic to molly fish and can cause stress, disease, or even death.
  • Nitrite: Similar to ammonia, the nitrite level must be kept at 0 ppm. Nitrite is also harmful to molly fish and can impair their oxygen-carrying capacity.
  • Nitrate: While not as toxic as ammonia or nitrite, high nitrate levels can harm molly fish. Aim to keep nitrate levels below 20 ppm for optimal health.
  • Water Hardness: Molly fish thrive in hard water with a general hardness (GH) between 10-30 dGH. They also prefer slightly higher carbonate hardness (KH), ideally between 7-15 dKH.
  • Temperature: Molly fish prefer warmer waters, so aim for a temperature between 72°F and 78°F (22°C – 26°C).

Also Read: Molly Fish Temperature

Essential Equipment For Molly Fish

Picking the right equipment for your molly fish tank is a crucial step when setting up the tank. Here is what you should know:

1. Filter

My recommendation: Fluval C4 Power Filter (link to Amazon).

A good quality filter is essential in a molly fish tank to remove waste and toxins from the water. It also helps in oxygenating the water and maintaining a balanced ecosystem.

Here are the reasons why filters are indispensable:

  • Waste Management: Filters trap debris and waste, preventing the buildup of harmful toxins which could harm molly fish.
  • Oxygen Supply: Filters aid in oxygenating the water, providing molly fish with the oxygen they need to breathe.
  • Biological Filtration: Some filters support beneficial bacteria, which helps in breaking down harmful substances like ammonia and nitrites.

Also Read: Do Molly Fish Need A Filter?

2. Heater And Thermometer

My recommendation: Orlushy Submersible Aquarium Heater (link to Amazon).

Molly fish require a specific temperature range to thrive. Therefore, a reliable heater and an accurate thermometer are essential to maintain the water temperature.

  • Temperature Control: Heaters allow you to maintain the water temperature within the 72°F to 78°F range, optimal for molly fish.
  • Thermometer Accuracy: A thermometer helps ensure that the heater is maintaining the correct temperature.
  • Preventing Health Issues: Proper temperature control helps prevent stress and illness in molly fish.

Also Read: Do Molly Fish Need A Heater?

3. Canopy And Lights

My recommendation: Hygger Aquarium LED Light (link to Amazon).

A tank cover or canopy, along with suitable aquarium lighting, is vital to mimic the natural environment and maintain a day/night cycle for molly fish.

  • Protection: A canopy prevents molly fish from jumping out and helps reduce water evaporation.
  • Lighting Control: Lights help simulate a natural day/night cycle, crucial for the well-being of molly fish.
  • Plants’ Health: Adequate lighting is also necessary for photosynthesis in live plants, which are beneficial for molly fish.

Also Read: Do Molly Fish Need Light?

4. Air Bubbler

My recommendation: Hygger Aquarium Air Stone (link to Amazon).

An air bubbler aids in the oxygenation of the water, ensuring the molly fish have enough oxygen to breathe:

  • Oxygen Supply: An air bubbler increases oxygen levels in the tank, essential for molly fish health.
  • Stimulating Water Movement: Bubblers also generate water movement, mimicking the molly fish’s natural environment.
  • Disease Prevention: Proper oxygenation helps prevent diseases that could arise from poorly oxygenated water.

Also Read: Do Molly Fish Need A Bubbler?

5. Air Pump

An air pump is crucial in conjunction with an air bubbler or air stone to aid in oxygenating the water for molly fish:

  • Enhanced Oxygenation: An air pump drives the air bubbler, improving the overall oxygen levels in the tank.
  • Equipment Backup: In case of filter failure, an air pump can help maintain some water movement and oxygenation.
  • Stability: Consistent oxygen levels provided by an air pump support a stable environment for molly fish.

Also Read: Do Molly Fish Need An Air Pump?

6. Aquarium Siphon And Mesh

My recommendation: Laifoo 5ft Aquarium Siphon (link to Amazon).

An aquarium siphon helps in cleaning the tank, and a mesh is important for handling the molly fish when required.

  • Efficient Cleaning: An aquarium siphon is used to remove debris and waste from the tank, ensuring a clean environment for molly fish.
  • Safe Handling: A mesh allows for safe handling of molly fish during tank cleaning or moving.
  • Disease Prevention: Regular tank cleaning using a siphon can help prevent diseases and stress in molly fish.

Aquarium Design And Foliage

The design and foliage in your aquarium play a central role in enriching the environment for your molly fish:

1. Plant Life

Introducing live plants to your aquarium not only enhances the aesthetics but also provides a natural habitat for your molly fish.

These plants offer much-needed hiding spots and improve water quality as well:

  • Pick the right plants: Molly fish thrive with compatible aquatic plants like the Java fern or Anubias. Make sure these plants will flourish under your aquarium’s lighting conditions.
  • Caring for your greens: A healthy plant needs appropriate lighting, fertilization, and carbon dioxide levels. These also contribute to oxygen supply in your tank.
  • Keeping things neat: Prune any overgrown or decaying parts of the plants to maintain a tidy look and to prevent other plants from being overshadowed.

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

2. Decorations

Apart from enhancing the look of your aquarium, decorations serve a functional role too, offering extra cover for your molly fish.

The right choice of decorations can significantly boost their comfort and wellbeing:

  • Choosing safe and smooth: Always go for smooth-edged decorations that are designed for aquariums to ensure your molly fish’s safety.
  • Creating hideaways: Position your decorations in a way that provides plenty of hiding places for your molly fish. This can reduce their stress levels and encourage their natural behavior.
  • Adding variety: A mix of natural elements like rocks, driftwood, or even caves can make the environment more interesting and visually appealing for your molly fish.

3. Substrate

The choice of substrate for your molly fish tank is crucial. It not only influences the growth of beneficial bacteria but also enhances the overall aesthetics of the tank.

  • Right substrate for the right purpose: Choose a substrate that facilitates plant growth and root development, like gravel or sand.
  • Keeping it clean: Make it a routine to clean the substrate with an aquarium siphon to prevent the build-up of harmful substances.
  • Considering plant needs: Always take into account the specific needs of your chosen plants when selecting your substrate.

4. Space

Molly fish love to swim around. So, it’s essential that they have enough space for unobstructed movement. This calls for a spacious aquarium.

  • Size matters: A minimum of a 20-gallon tank should be provided for your molly fish to freely explore and swim around. The bigger, the better.
  • Room for swim: Ensure plenty of open space in the middle of the tank to allow your molly fish to swim freely. Overcrowding the tank with decorations or plants could hamper their movement.
  • Up and down: Molly fish also enjoy swimming vertically. So, make sure to include tall plants or decorations that reach the water surface.

5. Lighting

The right lighting can help simulate a day-night cycle for your molly fish, supporting their natural rhythm:

  • Light choice: Pick lights that offer the correct spectrum and intensity for both your molly fish and the plants in your tank. LED lights are a great energy-saving option.
  • Sticking to the schedule: Mimic a natural day-night cycle by keeping a consistent lighting schedule. A good rule of thumb is to aim for 10-12 hours of light per day, followed by a period of darkness for the fish to rest.
  • No to over-lighting: Too much or intense light can stress your fish and encourage the growth of algae. So, be cautious with your lighting.

6. Elements Placement

Arranging your plants, decorations, and other elements in a strategic manner can create a pleasant environment for your molly fish:

  • Mimicking nature: Set up plants and decorations in a way that replicates the natural habitat of the molly fish. Grouping plants, creating different levels, and keeping open spaces for swimming can work wonders.
  • Creating functional zones: Create different areas for your molly fish to rest, hide, and explore by strategically placing caves and decorations. Also, ensure there’s enough swimming space at the center.
  • Safety comes first: Avoid using sharp or rough decorations that can harm your molly fish. Opt for smooth-edged or soft decorations instead.
  • Keeping it visible: Consider your viewpoint and that of your molly fish while arranging your tank. Taller decorations should go at the back or sides of the tank for a better view of your fish.
  • Balancing the aesthetics: Try to distribute your decorations evenly across the tank for a balanced and visually pleasing setup. Avoid cluttering or overcrowding specific areas.

Setting Up And Maintaining Your Molly Fish Aquarium

Setting up a molly fish tank from scratch is pretty straightforward. Simply follow these steps:

1. Conditioning The Water

Properly conditioning the water is crucial to creating a suitable environment for your molly fish.

Testing the water quality, adjusting pH if necessary, removing chlorine and chloramines, and maintaining an appropriate temperature are key steps:

  • Test the water quality: Use a reliable water testing kit to assess parameters such as pH, ammonia, nitrite, and nitrate levels. My recommendation: API FRESHWATER MASTER TEST (link to Amazon).
  • Remove chlorine and chloramines: Treat tap water with a dechlorinator to eliminate harmful chemicals.
  • Maintain appropriate temperature: Keep the water temperature between 75°F and 82°F for molly fish.
  • Adjust pH if necessary: Aim for a pH level between 7.5 and 8.5, as molly fish prefer slightly alkaline water.

Also Read: What Is The Best pH Level For Molly Fish?

2. Nitrogen Conversion And Beneficial Bacteria

Understanding nitrogen conversion and maintaining beneficial bacteria is essential for a stable aquarium ecosystem.

Cycling the aquarium, adding beneficial bacteria, and monitoring water parameters are important steps:

  • Cycle the aquarium: Allow the nitrogen cycle to establish before adding molly fish. This process typically takes 4-6 weeks.
  • Add beneficial bacteria: Introduce a bacterial supplement to populate the aquarium with nitrifying bacteria that aid in converting ammonia to nitrite and nitrate. My recommendation: Fritz Aquatics Nitrifying Bacteria (link to Amazon).
  • Monitor water parameters: Regularly test ammonia, nitrite, and nitrate levels to ensure they remain within safe ranges for Molly fish.

3. Feeding And Hygiene

Proper feeding practices and maintaining good hygiene are crucial for the health and well-being of your molly fish.

Providing a balanced diet, avoiding overfeeding, and performing regular water changes are important actions to take:

  • Provide a balanced diet: Offer a variety of high-quality flake, pellet, or frozen foods suitable for Molly fish, including vegetable matter.
  • Avoid overfeeding: Feed your Molly fish small amounts multiple times a day, only giving them what they can consume within a few minutes.
  • Perform regular water changes: Replace 10-20% of the aquarium water every 1-2 weeks to maintain good water quality and remove excess waste and toxins.

Also Read: How To Feed Molly Fish

Molly Fish Tank Tankmates

Peaceful freshwater fish of similar size make excellent tankmates for molly fish. Some suitable options include:

  • Platy fish (Xiphophorus maculatus)
  • Guppy fish (Poecilia reticulata)
  • Swordtail fish (Xiphophorus hellerii)
  • Neon tetra (Paracheirodon innesi)
  • Corydoras catfish (Corydoras spp.)
  • Cherry barb (Puntius titteya)
  • Harlequin rasbora (Trigonostigma heteromorpha)

On the other hand, avoid aggressive and territorial fish like:

  • Betta fish (Betta splendens)
  • Convict cichlid (Amatitlania nigrofasciata)
  • Jack Dempsey cichlid (Rocio octofasciata)
  • Red Devil cichlid (Amphilophus labiatus)
  • Tiger barb (Puntigrus tetrazona)
  • African cichlids (various species from the genus Cichlidae)
  • Oscar fish (Astronotus ocellatus)


Let’s quickly summarize the main points I covered earlier:

  • Molly fish thrive in spacious tanks of 20 gallons or more, reducing stress, preventing overcrowding, and providing ample room for swimming.
  • Maintaining stable water parameters (temperature, pH, ammonia, nitrite, nitrate) is crucial for the health and well-being of molly fish.
  • Essential equipment includes a quality filter for waste removal, a heater and thermometer for temperature control, a canopy or lights for a day/night cycle, an air bubbler for oxygenation, and an aquarium siphon for cleaning.
  • Aquarium design should incorporate live plants, smooth decorations, suitable substrate, and ample swimming space to provide hiding spots, cover, and a natural environment.
  • Proper setup and maintenance involve conditioning the water, establishing beneficial bacteria, feeding practices, regular water changes, and selecting compatible tankmates for molly fish.