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    How To Oxygenate A Fish Tank Without A Pump – Methods & Guide

    How To Oxygenate A Fish Tank Without A PumpPin
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    Want to keep your tank setup as low-tech as possible, so you’re going pump-free? Are you noticing signs of low oxygenation in the behavior of your pet fish? Learn how to oxygenate a fish tank without a pump quickly and efficiently!

    In emergency situations, you can increase oxygen levels inside your fish tank by pouring water from a height using a cup. You can also perform a 50% water change if oxygenation is dangerously low. This article will also go over various other methods.

    Increasing oxygen levels in your tank can become an emergency when you notice fish struggling to breathe, gasping at the surface. Changes in activity levels and fish gathering near the filter output can also indicate low oxygenation.

    If you’re just planning on skipping the air pump in your tank setup, there are plenty of ways to maintain adequate oxygenation.

    Poor aeration can take a serious toll on the life expectancy of your pet fish, increasing stress levels and wearing them down quickly. Algae will also thrive and drop oxygen levels even lower when there isn’t enough water circulation in the tank.

    Oxygenation Vs. Aeration – What’s The Difference?


    Before going into how you can efficiently oxygenate a fish tank without a pump, let’s make the distinction between oxygenation and aeration.

    Fishkeepers in the hobby often use these two terms interchangeably. And for good reason, as both of these processes have the same result: increased oxygen levels inside your fish tank.

    Oxygenation refers to the gas exchange itself, where water makes contact with atmospheric air at surface level. Water absorbs oxygen and releases carbon dioxide in a perpetual cycle. This gas exchange determines how much oxygen gets dissolved into the water.

    Aeration encompasses oxygenation but is linked to the movement of water (water flow/current) inside a fish tank. While oxygenation happens at the surface of the water, aeration will work to distribute oxygen-rich water throughout the entire tank.

    Aeration (water movement) is necessary to make oxygenation possible; that’s why stagnant waters have such low levels of dissolved oxygen.

    You can use dissolved oxygen test kits to test your fish tank’s oxygen levels:

    • Dissolved oxygen concentration in freshwater tanks should be 8mg/l or higher.
    • Dissolved oxygen concentration in saltwater tanks should be at least 7mg/l.

    Ways To Oxygenate Fish Tank Without A Pump

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    Red discus (Symphysodon discus)


    It’s common for fishkeepers to just prefer less plugged-in gear for their fish tank. Lower-tech aquarium setups have a more natural aesthetic, so it’s worth reevaluating your equipment once in a while. Air pumps are often the first to get dropped off the list of “essentials”.

    Air stones, hooked up to an air pump, will push tank water up, increasing the amount of water that gets oxygenated at surface level. The bubbles and movement improve aeration as well.

    Air pumps are considered basic equipment in the hobby, and few aquarists choose not to use them.
    If you do plan on going pump-free, keep in mind that maintaining safe oxygen levels inside your fish tank isn’t optional!

    Luckily there are several ways to increase oxygenation and create optimal aeration without installing an air pump. Even if you use a pump in a community tank, these ideas work well if you need to set up a quarantine/nursery tank. Sometimes there’s no room in a fishkeeper’s budget for additional gear.

    Add live aquarium plants

    Live aquarium plants are awesome oxygen boosters that also help reduce carbon dioxide/nitrate levels.

    If you feel intimidated by setting up a planted tank, choose beginner-friendly live plants to start off with:

    • Vallisneria;
    • Anubias;
    • Java Fern;
    • Amazon Sword;
    • Dwarf Hairgrass.

    You don’t even have to go full-jungle mode inside your planted tank to improve oxygen levels. Even a few midground plants will make a huge difference in how oxygenated your fish tank is.

    Carpet plants, like Micranthemum Monte Carlo, are also an excellent choice. They increase oxygen levels at the very bottom of the tank, where aeration is typically reduced. Because carpet plants grow in tight night bunches, oxygen levels will be high even without much water movement.

    Live aquarium plants won’t do much in terms of aeration throughout the tank. That’s why this water oxygenating method doesn’t work alone. You need to consider improving water circulation as well, so the water doesn’t remain stagnant.

    Keep in mind that even with low-maintenance plants, you’ll need to stay on top of your gardening duties. Trimming plants and removing rotting leaves is essential. Decaying plant matter can cause your tank’s biofiltration system to go haywire, plummeting the water quality.

    Use a strong filter with an adjustable flow rate

    To help with aeration in a planted tank, a strong filter with an adjustable flow rate is the best choice. You won’t be adding extra gear to your setup, and you’ll use the filter as a 2-in-1 subsystem.

    The intake/output water movement that a strong filter creates can be enough to maintain ideal aeration/oxygenation in an aquarium.

    You should, of course, consider the type of fish you’re keeping in said aquarium. Slow swimmers, or fish that generally prefer calmer waters, can get overwhelmed by the strong current.

    If you’re looking to oxygenate a betta tank without a pump, this isn’t exactly the right way to do it. But if your fish are active swimmers that like a challenge, go ahead and use a high flow filter to your advantage.

    Here are just a few fish species that will appreciate this type of tank setup:

    • Rasboras;
    • Barbs;
    • White Cloud Minnows;
    • Danios;
    • Hillstream Loaches.

    To maintain your filter’s high flow rate, make sure you clean it on a regular basis. Build-up gunk and debris can lower your filter’s efficiency.  

    Increase water surface agitation

    As oxygenation takes place at the water’s surface, breaking the surface tension will help oxygenate more water in the process. All the oxygen that your fish breathe comes from the gas exchange at surface level.

    Surface agitation facilitates oxygen absorption while also aerating the water to a certain degree.

    There are several ways to increase water surface agitation:

    • Waterfall filters

    Any type of filter with a pour-in output from a height will break the surface tension.

    Waterfall filters, spray bar systems, and even box filters all make excellent aeration boosters.

    The higher you set your surface agitation device, the deeper dissolved oxygen will make its way into your fish tank. This is a great way to oxygenate narrower & deeper tanks, cube aquariums, or nano tanks.

    Typically, your tank’s dimensions will dictate how much of the tank’s water is in direct contact with the air. But with increased water surface agitation, more water gets exposed to air, improving oxygenation. 

    • Lily pipes

    Crystal glass lily pipes are essentially pipes that you attach onto the filter’s output, to maximize the aeration inside your fish tank. These glass pipes are a treat for the eyes, as they don’t look like extra clutter, unlike plastic tubing.

    Here’s a visual of all the types of lily pipes that you can use to increase water surface agitation:

    Increase water surface area

    The more surface area a tank has, the more oxygen can get dissolved into the water through oxygenation. So, if you don’t plan on using an air pump, you should get a wider and shallower tank from the get-go.

    This is also the ideal aquarium shape if you’re going to keep labyrinth fish (bettas, gouramis, paradise fish). These fish use a labyrinth organ to breathe air at the water surface. They typically do this if oxygen levels drop too low or if the water quality is poor.

    A narrow and deep tank will be harder to oxygenate/aerate without an air pump. But with increased water surface agitation and a few live aquarium plants, oxygenation won’t be a problem.

    Keep fish that swim in different levels of the tank

    Overcrowding a fish tank can cause oxygen levels to drop, but if you can actually get your fish to help with water aeration in a way. Keep in mind that you should only stock your aquarium to a maximum of 85% of its capacity.

    Getting tank mates that are compatible but also occupy different parts of the tank is a good strategy. Get a mix of bottom dwellers, middle to top, and top to bottom swimmers, with a few surface feeders to cover all areas.

    Fish can help disperse oxygen-rich water throughout the entire aquarium as they go about their business. Fast swimmers and schooling/shoaling fish, in particular, will improve aeration greatly.

    Water changes/cup method (for emergency situations)

    If you’ve used a dissolved oxygen test kit, and the concentration of oxygen is dangerously low, it’s time to act fast. If you’re noticing that all your fish are desperately gasping for air, the problem usually requires emergency intervention. 

    In this case, to oxygenate a fish tank without a pump, you’ll only need a clean container (cup or jar). Take water from inside the aquarium (not tap water!) and slowly pour it back in from a decent height.

    Be careful not to take any of your fish along for this ride, as they will be hanging out at the water surface. The water might get cloudy for a while, as the aeration can dislodge debris.  

    Repeat the process a few times, and retest the dissolved oxygen concentration if possible.

    A 50% water change using dechlorinated water is an efficient, quick fix to poor oxygenation as well. 

    To prevent oxygen levels from dropping this low again, be sure to use one, or more, of the fish tank oxygenating methods listed above. Frequent dips in oxygen concentrations/water quality can cause fatalities among your pet fish!

    Signs Of Low Oxygen In A Fish Tank


    Testing water for dissolved oxygen levels is rarely part of a fishkeeper’s regular tank maintenance routine. Your fish will actually let you know if the water is poorly oxygenated.

    A sudden change in the behavior of your pet fish should always alert you, as even a small imbalance can trigger a cascade of issues. Low oxygen supply isn’t typically a problem in a well-established aquarium.

    Here are the key signs of low oxygen in a fish tank:

    • Labored breathing and gasping for air at the surface

    Some fish, like labyrinth fish or surface feeders, will “gasp” at the surface occasionally, and that’s completely normal.

    An alarming behavior is when fish remain at the water’s surface and continuously try to gulp more water from the surface.

    They do this because that’s the only area where the oxygen-rich water is when oxygen levels drop dangerously low inside the tank.

    • Fish move around less and change in swimming behavior

    In a self-conservation effort, fish will remain almost perfectly still when water is poorly oxygenated. They also tend to eat less, if at all. This behavior indicates that you need to take emergency measures (the cup method!).

    A change in swimming behavior, or activity level, can also be caused by poor water quality. You’ll know it’s a water oxygenation issue if the fish also display erratic gill movement. 

    • Fish gather near the filter’s outflow

    If just one fish is hanging out behind the tank’s filter, it might be feeling vulnerable because of a wound or a disease. Pregnant fish can also seek refuge in this area.

    This behavior becomes a warning sign of low oxygen if most of your fish are gathered near the filter’s outflow. Even when oxygenation is poor, this area will benefit from the aeration caused by the water current.

    Causes Of Low Oxygen In A Fish Tank

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    Ember tetra (Hyphessobrycon amandae)

    There are certain factors that can cause the concentration of dissolved oxygen in your fish tank to drop.

    • Overstocking

    Keeping too many fish in an aquarium can easily lead to an imbalance between oxygen absorption and carbon dioxide build-up. An overcrowded fish tank can have poor oxygen levels even when using an air pump.

    • Reduced aeration

    Insufficient aeration due to reduced water movement can plunge oxygen levels. Tank water that remains stagnant will also pave the way to algae overgrowth.

    • A build-up in the filtering system

    Clogged filters and waste-covered filter media will drastically reduce the efficiency of your filtering system. Not only does this negatively impact water quality, but it also slows down the filter’s flow rate.

    • A sudden increase in water temperature

    Whether your heater’s malfunctioning or your tank’s getting too much direct exposure to sunlight, a spike in water temperature will cause oxygen levels to drop.

    Live aquarium plants are oxygen suppliers when their basic needs are met. Plants won’t convert carbon dioxide into oxygen if you’re not keeping the lights on for at least 6-8 hours per day. This can also happen if the lighting is too low.

    • Dosing medicine

    Some over-the-counter fish medicine can temporarily cause reduced oxygen levels.

    Solution To Low Oxygen In A Fish Tank


    You can use any of the methods listed above to oxygenate a fish tank without a pump if dissolved oxygen levels are low. Once the issue is resolved, the goal should be to keep water oxygenation stable.

    Like with other water parameters (pH, temperature), it’s difficult to chase a perfect value within the recommended range.

    In reality, having stable tank conditions is much more important than getting a perfect read on a test kit. Small fluctuations are to be expected.

    At a reasonable stocking capacity, an established planted tank can easily maintain ideal oxygen levels without a pump!

    Signs Of Too Much Oxygen In A Fish Tank

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    Corydora catfish (Corydoras delphax)

    You can’t exactly over-oxygenate the water inside a fish tank. What can happen is that with too many oxygenators in the mix, you can cause too much water agitation.

    If the water current is too strong, or your fish don’t have enough refuge areas from the constant water agitation, stress levels can skyrocket.

    • Fish struggling to swim

    Fish that are native to slow-moving, almost stagnant waters can get overwhelmed by excessive water circulation. Bettas, for example, are not big fans of filters with high flow rates. 

    Having bubbles, air stones, and a filter all running continuously can create too much water turbulence. If you notice fish getting thrown about by the current, it’s time to cut back on aerators.

    • Gas bubble disease

    This is a non-infectious condition that’s typically caused by trauma. A sudden change in pressure (too much oxygenation) can cause fish to get bubbles in their gills, in their eyes, and near their fins.

    Causes Of Too Much Oxygen In A Fish Tank


    • A filter that’s too strong

    Your filtering system is either too strong or has too high of a flow rate for the size of your fish tank.

    • Too many aerators

    There are too many aeration devices in the same aquarium (bubblers, air pump, wavemaker, filter’s outflow, etc.).

    Solution To Too Much Oxygen In A Fish Tank


    You should get an appropriately sized filter, preferably with an adjustable flow rate.

    Remove aeration devices one at a time until you settle on a setup that keeps aeration/oxygenation at an optimal level.



    You can definitely skip the pump when setting up your aquarium, especially if you’re set on a planted tank.

    You can efficiently oxygenate a fish tank using a combination of oxygenation and aeration-boosting methods.

    Start off with a wider, and shallower, fish tank to get a head start in pump-free oxygenation.

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