Do Molly Fish Need An Air Pump? (And Which One Is Best)

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Molly fish, along with other fish species, rely on extracting oxygen from water in order to breathe. Their gills play a crucial role in this process by drawing in water and extracting the oxygen it holds.

While certain fish possess lung-like structures enabling them to gulp air from the water’s surface, the primary source of oxygen for fish is dissolved in the water.

In natural environments, oxygen levels are typically plentiful. However, in aquariums, it becomes the fishkeeper’s duty to ensure adequate aeration for the fish.

How Oxygen Transfer Works In Aquariums

In aquariums, oxygen transfer happens at the water’s surface where air oxygen dissolves into water, providing crucial oxygen for fish like molly fish.

This process relies on factors like water temperature, salinity, and movement. Devices like air pumps and filters are commonly used to assist this process.

Here are key factors to consider:

  • Surface area and movement: More surface area and movement increases oxygen absorption. In a molly fish aquarium, a water pump might create waves, increasing the oxygen exchange area.
  • Water temperature: Higher temperatures decrease water’s oxygen capacity. For molly fish, preferring 25-28°C, effective oxygen transfer ensures they can breathe in warmer water.
  • Plants’ role: Aquatic plants produce oxygen during photosynthesis. An aquarium for molly fish might include plants like Java Moss or Anubias, enhancing the oxygen supply.
  • Mechanical devices usage: Devices like air pumps and filters increase the water’s oxygen content. For molly fish, an air pump creates bubbles, enhancing water movement and oxygen absorption.
  • Salinity levels: Higher salinity reduces water’s oxygen capacity. For brackish molly fish, living in higher salinity, oxygen transfer must be closely monitored.

Do Molly Fish Need An Air Pump?

While molly fish are resilient and adaptable, they don’t necessarily require an air pump to survive in an aquarium.

However, using an air pump can significantly enhance their environment by improving oxygenation and water movement, which can contribute to their overall health and wellbeing. 

An air pump aids in creating a conducive aquatic environment, contributing to the quality of life of molly fish, especially when kept in larger groups or more densely populated tanks.

Here is what you should know:

  • Oxygenation Enhancement: The use of an air pump increases the oxygen level in the aquarium. Given that molly fish thrive in well-oxygenated water, this can make a huge difference to their comfort and health, thereby extending their lifespan.
  • Water Circulation: An air pump improves water circulation, ensuring that oxygen is evenly distributed throughout the tank. For molly fish that prefer swimming in various water levels, this consistent circulation is vital to providing them with an oxygen-rich habitat, regardless of their position in the tank.
  • Waste Management: Air pumps contribute to better waste management by breaking down the surface tension and pushing organic waste towards the filter. This leads to a cleaner environment for molly fish, reducing the risk of disease and stress.
  • Stimulates Natural Environment: Air pumps can create a current, mimicking a molly fish’s natural riverine or coastal habitats. This helps to keep the molly fish active and stimulated, promoting natural behaviors and contributing to their overall well-being.
  • Beneficial for Live Plants: If your molly fish tank includes live plants, air pumps can aid in their growth by enhancing photosynthesis. Healthy plants not only enrich the aesthetics but also contribute to better water quality, providing a healthier environment for molly fish.

Also Read: Molly Fish Tank Setup

Some Other Aeration Devices You Can Use

Even though air pumps have their benefits, there are some alternatives when it comes to molly fish:

1. Filters

Aquarium filters serve dual purposes – they maintain water cleanliness and enhance aeration.

By drawing water in and releasing it back, the water flow creates movement and enriches the tank with oxygen, beneficial for aquatic residents such as molly fish:

  • Mechanical Action: The suction and discharge actions of filters contribute to water movement, enhancing the oxygen dissolution rate. This creates an oxygen-rich environment for molly fish.
  • Biological Filtration: Beneficial bacteria in filters break down harmful substances like ammonia, produced by molly fish, into less harmful substances, aiding in tank health.
  • Chemical Filtration: Filters also help remove harmful dissolved substances that could impact water chemistry and the health of molly fish.

2. Powerheads

Powerheads, a type of water pump, provide excellent water movement and aeration in the aquarium. They mimic natural currents, which molly fish experience in their wild habitats.

Here is what you should know:

  • Strong Currents: Powerheads create strong currents that agitate the water surface, enhancing oxygen absorption which is beneficial for molly fish.
  • Versatility: They can be positioned anywhere in the tank, providing consistent water flow and oxygen supply throughout the aquarium, benefiting the molly fish.
  • Stimulation: The created water currents stimulate molly fish, encouraging more active behavior and enhancing their overall health.

3. Spray Bar Aerators

These devices disperse water in a spray or jet, creating surface agitation which facilitates gas exchange. This is important for providing molly fish with an oxygenated environment:

  • Improved Aeration: The spraying action of these aerators breaks the water surface tension, enhancing the oxygen dissolution rate, beneficial for molly fish.
  • Versatility: Spray bars can be adjusted to direct flow at various angles, helping distribute oxygen uniformly, an advantage for all tank inhabitants, including molly fish.
  • Quieter Operation: They typically operate quietly compared to air pumps, reducing stress on sensitive species like molly fish.

4. Air Bubblers

An air bubbler is a device used in aquariums to enrich the water with dissolved oxygen. Molly fish thrive in well-oxygenated waters, and air bubblers ensure this condition is met, thus promoting their health and well-being.

  • Enhances oxygen levels: Air bubblers facilitate the circulation of air in the water, increasing the oxygen levels.
  • Promotes water circulation: Besides oxygenation, air bubblers help in promoting water circulation. This reduces stagnation, which molly fish do not prefer, and encourages their active behavior.
  • Aesthetic appeal: Finally, air bubblers can also add to the visual appeal of the aquarium. The constant flow of bubbles provides a mesmerizing effect, creating an attractive environment for the molly fish and the onlookers.

Also Read: Do Molly Fish Need A Bubbler?

How To Increase Oxygen Levels In Molly Fish Tanks Without An Air Pump

There are a few ways to increase the oxygen levels in a molly fish tank even without an air pump:

1. Using Live Plants To Enhance Oxygen Production

Live plants can significantly help in maintaining the oxygen level in a molly fish tank, thanks to their photosynthesis process.

They absorb the carbon dioxide that the fish produce and, in turn, generate oxygen that benefits your molly fish.

A variety of aquatic plants are suitable for molly fish tanks, including Hornwort, Anubias, and Java Fern.

These plants not only improve the oxygen level but also provide shelter and breeding grounds for your molly fish.

Here are some things to consider:

  • Choice of Plants: Choose plants like Hornwort, Anubias, or Java Fern that are known for their high oxygen production and suitability for molly fish tanks. These plants can help maintain an oxygen-rich environment.
  • Proper Lighting: Ensure the aquarium has enough light, ideally natural sunlight or a dedicated aquarium light for about 8-12 hours a day. It’s essential for photosynthesis, which increases oxygen production.
  • Regular Pruning: Regularly prune the plants to ensure healthy growth and maximum oxygen production. Overcrowding can lead to poor light penetration and reduced photosynthesis, affecting oxygen levels.
  • Balancing Plant-Fish Ratio: Maintain a balance between the number of plants and molly fish in the tank. Too many fish can overwhelm the plants’ oxygen-producing capabilities.

2. Proper Water Filtration

Proper water filtration is crucial to maintaining the right oxygen level in molly fish tanks. 

Filtration systems not only remove impurities but also improve water circulation, which enhances oxygen exchange.

An effective filter system, such as a hang-on-back (HOB) filter or canister filter, can significantly aid in maintaining the optimal oxygen levels for your molly fish.

My personal recommendation is the Fluval 207 Canister Filter (link to Amazon). Here are some points to keep in mind:

  • Choosing the Right Filter: Depending on the tank size, a hang-on-back (HOB) filter or canister filter can be highly effective. These filters ensure proper water circulation, promoting oxygen exchange.
  • Positioning of Filter: Position the filter outlet near the water surface. This way, water agitation increases, leading to better oxygen-carbon dioxide exchange beneficial for molly fish.
  • Regular Filter Maintenance: Regularly clean and maintain the filter to keep it functioning effectively. A blocked or malfunctioning filter can disrupt water flow and oxygen levels.
  • Avoid Overcrowding: Overcrowding can lead to more waste, increasing the burden on the filtration system. Maintain an appropriate number of molly fish per gallon to ensure optimal conditions.

3. Perform Regular Water Changes

Regular water changes are another effective way to increase oxygen levels in molly fish tanks.

By replacing a part of the tank water, you help remove waste and toxins while adding fresh oxygenated water.

The general guideline is to change 10-20% of the water every week for a molly fish tank. Keep this in mind:

  • Water Change Frequency: Perform regular water changes, ideally changing 10-20% of the water every week. It helps maintain optimal oxygen levels for your molly fish.
  • Avoid Complete Water Changes: Never replace all of the water at once, as it can shock the molly fish and disrupt the established bacterial colonies essential for a healthy tank environment.
  • Water Temperature: Ensure that the new water is of similar temperature as the tank water to prevent temperature shock, which could stress the molly fish and reduce their oxygen intake.
  • Use of Water Conditioners: Use a water conditioner during water changes to neutralize harmful chlorine, chloramines, and heavy metals in tap water, providing a safer environment for your molly fish. My recommendation: API Tap Water Conditioner (link to Amazon).

Air Pump Options For Molly Fish

You don’t need anything fancy when it comes to an air pump for your molly fish. One popular choice would be the Tetra Whisper Air Pump (link to Amazon).

There is a range of air pumps to choose from, such as diaphragm pumps and rotary vane pumps.

The choice depends on the size of the tank, the number of molly fish, and the overall setup. Here are some important considerations when selecting an air pump for your molly fish tank:

  • Tank Size and Pump Rating: Select an air pump that matches your tank’s size. For instance, if you have a 20-gallon tank, an air pump rated for 20 gallons would usually suffice. However, if you plan to operate additional equipment like air stones or sponge filters, consider a pump rated for larger tanks.
  • Use of Air Stones or Bubble Wands: These can be connected to the air pump to create finer bubbles, which increases the water surface area for oxygen exchange. This is beneficial for the molly fish as it helps increase the oxygen concentration in the water.
  • Noise Level: Air pumps can sometimes be noisy. Look for pumps with soundproofing features or those known for quiet operation, so as not to disturb the peaceful environment for your molly fish.
  • Backup Power Supply: Considering an air pump with a battery backup can be a lifesaver for your molly fish during power outages. This ensures that the oxygen supply isn’t interrupted, keeping the molly fish safe.
  • Regular Maintenance: Regardless of the type of air pump, regular maintenance is crucial. Clean and check the pump regularly to ensure it is functioning efficiently and providing adequate oxygen for your molly fish.


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

  • Oxygen transfer in aquariums relies on air oxygen dissolving into the water’s surface, providing vital oxygen for molly fish and other aquatic species.
  • Factors like water temperature, salinity, and movement significantly impact the efficiency of oxygen transfer in aquariums, emphasizing the need for careful consideration of these factors.
  • Air pumps and filters, commonly used in aquariums, play a crucial role in increasing water movement and oxygen content, enhancing the oxygen transfer process for the well-being of molly fish.
  • Aquatic plants, such as Java Moss or Anubias, contribute to oxygen production through photosynthesis, making them valuable additions to a molly fish aquarium to improve the oxygen supply.
  • While not essential, using an air pump in a molly fish tank can greatly benefit their environment by enhancing oxygenation, water circulation, waste management, simulating natural habitats, and supporting the growth of live plants, ultimately promoting the overall health and well-being of the fish.