Fish swimming up and down in the aquarium is a sign that your fish is unhappy and stressed. If there is any issue in the tank, fish will start surfing up and down, which is called “glass surfing.”

If your fish is continuously showing this behavior, you need to address this before more severe problems like injury or illness arise. Here in this blog post, you will learn why your fish is swimming up and down and the six most common reasons behind it.

Why Is My Fish Swimming up and Down?

Fish exhibit this behavior to tell us about how they are feeling. When fish move periodically up and down, this indicates that something is wrong with them, such as not being happy in their environment. There might be some stress or any other reason.

Being an aquarium keeper, the first thing that comes to mind is to examine the situation thoroughly – going through tank and water conditions as well as the fish’s diet and tank mates — and find what could be causing this much distress. If you diagnose the problem, there might be something you can do about it.

In most situations, the major cause behind this problem is a poor choice of stocking and tank size. These are some of the biggest reasons why aquarium fish go too soon, which is all due to that pesky anxiety. So, before bringing any new inhabitants into the aquarium, make sure that they’ll be cared for properly by researching all aspects, including dietary needs and space requirements.

In the next section, we will explore the 6 most common reasons why your fish is swimming frantically in the tank.

– Overstocking

Overstocking is a common mistake that many people make when they get fish for the first time. Usually, aquarium keepers put more than the recommended amount of fish in the tank and don’t realize how much space each fish requires. An overstocked aquarium is difficult to care for and affects the quality of life of its inhabitants. Overstocking can also affect the quality of water in a tank, so most fishes become stressed.

Cloudy water can mean that your tank is not equipped with enough filtration to keep up with the amount of waste being produced by fish. Fish produce a lot more than just excrement, so if there are too many fish in one place, they’ll start making dirty clouds, and you have to filter the water more often or decrease the number of fish in the tank.

Otherwise, overcrowding can lead to all sorts of problems, including disease and even death. Under this kind of stress, the fish’s immune system becomes weak, making them more susceptible to getting sick in general.

You’ll notice that different fish have their own personality traits. Some are more active than others; some stay in certain tank areas and will not venture too far. Others prefer a solitary lifestyle where they lie on top. But when there is overcrowding, your fish will start pacing up and down around the glass. Fish need space to swim, and when they do not find the desired amount, it can have a detrimental effect on their health.

– Overfeeding

When there are many fish in the tank, you will need to feed them more, and their food waste will increase at the bottom. However, many microbes come with the fish and live in the tank. These helpful creatures help process waste and keep everything running smoothly.

When the food load at the bottom increases and the microbe colonies can’t handle all of the waste, they quickly foul the tank water. Similarly, algae and pest snail outbreaks can also be a big problem when too much uneaten food is in the tank. So, as the water quality gets worse and food starts to decay, you will see your fish swimming up and down against the glass.

In this case, you should attack the problem on two fronts: on the one hand, make sure you give your fish just as much food as they can eat in a few minutes. On the other hand, make sure you clean the water often and that the filtration system works properly.

– Poor Water Quality

Poor quality water disturbs the ecosystem of the fish that they require for healthy growth. It is observed that almost 90 percent of the problems in the tank are due to poor water quality and lack of maintenance. Inadequate water quality suppresses the fish’s immune system, and there will be more chances of disease getting hold of the tank.

Every fish keeper knows that if they have a tank with water in it, sooner or later, the chemicals will take over the tank and make the water dirty. In order to reduce these unpleasant odors, you need proper cycling before adding any new inhabitants.

Aquarists need to manage water quality in an aquarium through filtration, regular water changes, and treatments. Aquariums also require maintenance like feeding carefully supervised diets and maintaining water temperature. If you keep all the parameters in check, there are fewer chances of buildup problems, and you will not find your fish swimming frantically in the tank.

The best way to check if your tank has healthy water or not is by water testing. Straight away, take the water to the nearest fish store, and they will test it for you. Remember that it’s best to test the water from time to time, and for 100 percent safety, check your water source. You will also find different easy-to-use and inexpensive kits that can tell the water health in no time.

– Unsuitable Tank Mates

If you want to make sure your fish swimming erratically finds some peace, you will have to choose the suitable tank mate for them. A good tank mate can make a visible difference in the life of your fish.

It would help if you also did not put together combinations that could be stressful or harmful for the tank inhabitants. If you put the wrong combination, there will be constant bullying or fighting, and you will find your fish swimming against the glass.

There’s a lot that goes into choosing the right fish for your tank mate. You’ll have to do some research and pick out just what they need, and there is zero chance of going wrong with your decision if you perform proper research.

If you get the wrong combination, instead, the aggressive fish will have a hard time if kept with a gentle creature. They may constantly be on edge and stressed out from being around an irritable individual who never gets any peace or relaxation.

– Water Temperature

Maintaining the proper temperature is essential for all types of fish. As you know, fish are ectothermic or cold-blooded creatures, which means they have no control over their body temperature. Instead, they depend on outside water temperature to control their activity and metabolism.

Keeping your fish in the required temperature range will keep them happy. If the temperature is too high or too low, ultimately, your fish will suffer. If your fish feel too cold, their activity increases and you will see your fish swimming fast back and forth. In those conditions, their immune system becomes compromised, and they become more prone to different health problems.

If the water temperature is too high, their breathing and metabolism will shoot up and use more oxygen. The problem with warm water is that, as the temperature rises, its oxygen holding capacity decreases. In such circumstances, you will find your fish swimming in one spot.

Each fish has a different temperature requirement, and it mostly depends on which part of the world they are native to. Some creatures thrive in cold regions, while others can’t survive without heat. Always select a fish after getting complete knowledge about them.

– Size of the Tank

The size of the fish tank is the critical factor in how your fish will think about its home. Most people believe that the bigger the tank is, the better it is for their fish, but that is not always true. The main thing is the correct number of fish and the right environment, which makes the difference between happiness and stress.

However, it is true that your fish should have enough space to thrive. If you keep fish in a small tank, you can easily see that the fish will always seem stressed. The limited space of the tank makes them uncomfortable, and they will not grow properly.

Another problem with small tanks is that they are difficult to maintain as compared to larger ones. The water quality and temperature are more likely to dangerously oscillate, and even a small amount of waste can make the water dirty in no time. If this happens, you will see your fish swimming up and down, uncomfortable against the glass.


There are many reasons why fish swim up and down. We have covered a lot of ground on this topic, so let’s summarize to make sure you will get the best information when it comes to keeping your fish happy or healthy.

As a general rule, fish swim up and down when they are under stress. This can be due to:

  • Overstocking, causing extreme stress as your fish won’t have enough space to swim.
  • Overfeeding, which in turn results in extra waste in the water, deteriorating the environmental conditions.
  • Poor water quality, with the presence of elements which could potentially harm your fish.
  • Unsuitable tank mates, bullying your fish or trying to engage them in a fight.
  • Incorrect water temperature, putting the immune system of your fish under increased stress.
  • Incorrect size of the tank, exacerbating the problems mentioned above.

Fish swimming up and down in the tank is an indicator through the behavior that water quality is not correct or there is any other problem in the tank. You have to find that problem and solve it, and your fish will be happy again in no time.

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