Why Your Fish Is Swimming At The Top of The Tank

Why Your Fish Is Swimming At The Top of The Tank

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Poor water chemistry and general off-environments are part of the reason most fish keepers lose their fish. And while some parameters are hard to tell when they are not ideal for your aquatic pets, others are pretty obvious, more so when your livestock lets you know something is off.

One way your fish exhibits uneasiness is swimming at the top or bottom of the tank, erratic movements, glass surfing, and in dire cases, gasping. Obviously, there are some species like betta that like hanging out near the surface, but not too much and definitely not coupled with gasping.

Usually, your aquarium fish will swim at the top of the tank when there is not enough air in the water for them to live on. Usually, this behavior is coupled with your animals heaving on the waterline, trying to catch a breath.

From experience, the easiest way to resolve this is to add an air pump to your fish tank and make sure it is an adequate size for the setup you have. If looking for a quiet unit, the tetra whisper has proven to be a reliable unit over and over, with maximum airflow and various sizes for whichever aquarium.

Please read on for more insight on the top, plus why your fish might be swimming at the bottom of the fish tank.

Why Your Fish Are Coming to The Water Surface

Low oxygen concentration in your tank will cause your aquarium to fish to swim to the surface, closer to the waterline where there is better aeration. Though in lesser cases, this behavior might be caused by bad water quality, which results in a high ammonia concentration.

As such, the first thing you want to do is make sure your aerators, including airstones and air pumps, are functioning as expected. Of course, if you do not have any aerators in your aquarium, adding them would be the smart thing to do.

However, there is a chance your fish might be gasping at the surface due to other reasons. So, once you’ve eliminated low oxygen as a cause, consider other possibilities such as low water conditions, temperature, ammonia, or excess nitrates.

Please note that there are some species of fish such as betta and gouramis, which have a labyrinth organ, meaning they can breathe at the water surface. If keen, you’ll notice them swim to the surface, take on some air, then swim back into the water.

With labyrinth fish, you should only be concerned if the fish is gasping and spending too much time near the water surface.

Fish At The Top of The Tank After Water Change

Regular small water changes are recommended to ensure your fish tank remains safe and healthy for your fish. Even so, you should avoid large replacements or changes that overly shift your water parameters.

Any massive water change, especially combined with a filter or gravel changes (or cleaning) will cause your tank to go through a mini-cycle.

The secondary cycle will then cause drastic variations and shift your water chemistry, causing your fish to suffer, maybe even swim to the top. Almost like they are trying to get out of the tank, away from the misery.

Ammonia and nitrites spikes may also occur, damaging your fish’s gills, which will further cause them to gasp and swim close to the surface .

Quite often, fish keepers lose fish this way.

So, what is the right way to do water changes, you might ask.

Well, about 10 to 15 percent (20 at most) water changes once every week to a fortnight is recommended. The new water should have similar parameters to those you fish are used, more so the ph, temperature, and overall clarity.

You will also want to dechlorinate and condition your fish tank water to remove any off elements that are harmful to your fish.

Reverse osmosis is also not very safe when keeping fish that prefer alkaline water like African cichlids. As such, remineralize it to improve these parameters.

Lastly, if you realize that your tank is going through a mini-cycle and ammonia and nitrites levels are rising, I would suggest doing frequent up to 25 percent water changes with additional prime until the levels go down.

New Fish Swimming At The Top of The Tank

Other than low oxygen and ammonia spikes in your fish tank, new fish might swim at the top of the aquarium (near the water surface) if the chemistry is substantially different from what they were used to in the pet shop.

This is especially true if you fail to acclimate your fish correctly.

In lesser cases, new fish in your tank may swim near the surface if there is a bully in your aquarium, and not enough plants, decorations, and caves for the newbie to hide. Or maybe the fish came into the new environment with an ailment making it weakly, stressed, and coincidentally, more susceptible to attacks.

Fish Not Moving At The Top of The Fish Tank

Now, this statement can be interpreted in a couple of different ways.

First, your fish might be immobile at the top of the tank but still be visibly alive. For instance, if the gills are moving, it means the animal is still breathing.

In which instance, the most probable scenario would be severe stress on your fish, most likely due to poisoning by toxic water, which results in lethargy and lesser activity.

A sick fish will also have reduced movement as all its energy is directed to fighting the ailment, with little left for other activities.

Intrestingly, this would be one of the better scenarios, because then you can intervene and save your fish. Start by checking your water parameters, then make sure your aquatic friend is not battling an ailment.

That said, the second and quite dire scenario would be that you fish is dead…

…and yes, dead fish often float to the top of the tank.

Even so, a dead fish will more likely sink as soon as they die because they are denser than water, then become more buoyant and float as bacterial decomposition produces gases inside the body.

Plus the corpse will stink, so it should be pretty easy to tell if your fish is still alive, given the timelines of floating to the top and the odor.

One other scenario to consider is your fish is resting or sleeping. Usually, if your fish is taking a nap, it will remain relatively still, but the fins and gills will be moving to keep the fish alive and steady.

But please note, only top-dwelling fish will rest at the top. Those that prefer mid and bottom water levels enjoy their naps in the same area they like to swim.

Moreover, most tropical fish follow the diurnal cycle, where they are active during the day and sleep at night when the lights go out. So, if your fish is sleeping during the day, you might want to make sure its ok, especially if it’s not a nocturnal species like kuhli loach.

Fish At The Bottom of The Tank Not Moving

There are a couple of aquarium fish that prefer to stay at the bottom of the tank, including plecos, catfish, loaches, and cichlids, and quite a number of them are pretty lazy and don’t move much.

As such, do not be too alarmed if your loaches and catfish rest (remain relatively motionless) or hide during the day. Just make sure they are not gasping or completely immobile.

If they are panting, looking restless, or lifeless, then you should consider checking your water. Most likely, there is not enough oxygen at the bottom of the fish tank, which is very possible if you do not have an air pump-air stone system and only depend on your filter for aeration.

The second possibility would be if your water chemistry is off, more so after a water change or cleaning your tank. Not doing enough changes and tidying up may also result in ammonia spikes with the same effect on your fish.

Ammonia poisoning is especially lethal and kill your fish. So, if you notice your fish showing signs that of your water being toxic such as the fish gasping, breathing slowly, or remaining motionless, test your water and take the necessary step to remedy the situation.

The short term solution would be to clean your fish tank and perform a moderately large water change. The long game is to add more plants in your fish tank, plus make sure it’s not overstocked.

Feeding your fish less often and cleaning any leftover (and other organic waste) will also go a long way toward making sure your fish remains safe.

How To Oxygenate Your Fish Tank

We’ve already established that part of the reason your fish might be swimming at the top (or bottom) while remaining motionless for long could be insufficient oxygen.

So, the million-dollar question is, “How do you oxygenate your fish tank.”

The fastest way to aerate a fish tank is by adding an air pump in the tank. Usually, it’s coupled with air-stones units, which deliver the oxygen into the tank.

However, some hobbyists just use an airline tube to deliver the extra air, especially in small uncomplicated setups.

Just make sure you get an air pump unit that’s adequate for the size of the fish tank you have.

In smaller, lightly stocked tanks, using a powerful filter that creates a lot of water movement, such as canister and power units, adding an air pump might not be necessary. You can quite readily achieve the same effect by increasing your filter’s flow rate.

Another easy way of adding oxygen to your fish tank is adding more live plants because they are known to take up carbon dioxide and release oxygen at certain times of the day.

Morevoer, live aquatic plants also consume nitrogen, which they retrieve from nitrogen-compounds such as ammonia and nitrite, two elements that are abundant in aquarium ecosystems and need to be continuously expelled.

One last trick that will help ensure you have sufficient oxygen in your aquarium is making sure you only have the number of fish recommended for your tank size; avoid overstocking.

Can You Over Oxygante Your Fish Tank

Ridicoulus as it may sound, YES, it is possible to over oxygenate a fish tank, which causes air bubbles in your water, and cause gas-bubble-disease in fish.

However, you will more likely have less than more oxygen in your fish tank.

To make sure you do not have too much in your aquarium, I recommend only using an air pump that’s rated for your fish tank size. If you realize too much air (or air bubbles) in your water, reduce your air-units flow rate.

Also remember to take into account the air getting to your fish tank via your filter process or the waters' contact with ambient air.

Lastly, be careful while using air stones to aerate your fish tank because you risk introducing bubbles in the water, which are not always fish friendly.

Although they’ll add oxygen to your tank and keep water circulating, you want to place them strategically, like at the bottom, where there is limited aeration from the surface.

Placing your airstone in an area with sufficient water circulation is an ideal hack to keep the bubbles moving and sucked out of the water readily where need be.

Thats all. See you on the next one.

Happy fish 🦐🐠 keeping.

Eddie Waithaka

Resident Content Creator and Marketer at AquariaWise who talks about aquariums and fish and aquascapes a lot.

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