Why Is Your Fish Bouncing at The Bottom of The Tank?

Fish are calm creatures that usually swim or float effortlessly around their aquarium or hide between caves and stones.

It is a rare occasion to see them swimming frantically, being lazy, or not moving around at all. Of course, lack of energy or being more lethargic or relaxed all happen every now and then but in general, these are rare occurrences.

Sometimes fish can rub themselves against the tank’s walls or bottom if they are itchy. Frantic swimming might appear if the water flow in the aquarium is too strong, or the fish is under stress for one reason or another.

Bouncing back at the bottom of the tank, also known as flashing, is another behavior that could happen. This, however, is not a normal activity and might be the result of parasitic infestation. High ammonia or nitrate levels, low oxygen levels, improper temperature or a high or low pH can also cause flashing. Incorrect salt levels in saltwater tanks might also be a reason for such behavior.

Bobbing is similar to bouncing – it is when the fish cannot stay balanced in the water or upright. A reason for this could be a swim bladder disease that makes the “jump” back and forth in the water, bouncing up and down.

Amongst other reasons for bouncing might be poor tank conditions such as inappropriate size, stress, unhealthy water chemical balance, and wrong temperature.

Let’s explore all possible reasons in more detail:

Poor Water Conditions

Providing a clean, healthy, and friendly tank is the number one condition you have to fulfill as a fish owner. Waste that builds up, improper cycling, and even the wrong tank size can also be contributing factors to your fish bouncing up and down. It means that your aquatic friends are not comfortable with something.

Make sure you perform frequent water changes to avoid waste piling up. Clean the gravel and all decorations as food remnants and uncleanliness sticks on them as well.

In case you don’t know if the water is healthy enough, take a sample and bring it to the local pet store. The water will be tested there, and you will hear what is needed easily.

Affordable test kits are also available on the market that you can use at home. The levels of ammonia, nitrite, nitrate, and pH are easily tested with them.

Overstocking and Overfeeding

Food is good but not when it’s more than necessary. Large amounts of food in your fish might make it heavier than normal, thus causing a loss of balance and inability to swim straight in the water.

If you are a starter, research carefully the type of fish you’re buying, what food, and in what quantities of it the fish needs, precisely.

Overstocking basically means a crowded aquarium. The fish in the tank are one thing but there are many microbes that live in the water. This is a good thing; they help process the waste created by the fish. And therefore, the tank is cycled – to help increase the number of healthy microorganisms. However, when there are too many fish, things can get out of control.

The more fish there is, the more waste is created. Then the microbe colonies cannot catch up to process the impurities fast enough. As a result, decaying food starts to build up in the tank causing toxic waters.

Incompatible Tank Mates

Another reason for your fish bouncing at the bottom of the tank might be the presence of incompatible tank mates. If your fish co-habits with other fish and they don’t get along, your aquatic fella might bounce out of frustrations. Imagine yourself being locked up in a small space with someone you don’t like!

This is another thing that you have to research very well when buying a fish – its compatibility with other kinds of fish.


Another reason for your fish bouncing at the bottom of the tank, and unfortunately, a very likely one, is the presence of parasites. The most common types of parasites in freshwater are monogenean trematodes, and the protozoa Trichodina Ichthyophthirius, Costia, and Chilodonella.

All of these are microscopic parasites and require a veterinarian’s expertise to diagnose the correct parasite.

Parasite infestations are particularly common when a new fish is added to the aquarium or live plants that have not gone through a quarantine period.

For the veterinarian to examine your fish and make a proper assessment, they will have to: asses the tank size, the number of fish, the filtration system, water quality, and finally examine your fish.

During the physical exam, the vet will take a small sample of skin mucus and gills. These samples will be checked under a microscope and a diagnosis will be determined.


The best way to protect your fish from current and future infections is to place any new inhabitants under quarantine for 4-6 weeks before introducing them to the tank.

This is enough time to eliminate potentially harmful bacteria and prevent them from entering the tank via the new fish.


In short, your fish may be bouncing in the aquarium for several possible reasons such as:

  1. Parasite infestation
  2. Poor water conditions
  3. Wrong tank size
  4. Incompatible mates
  5. Overstocking
  6. Overfeeding.

If you notice your fish bouncing up and down at the bottom of the tank, the first thing to do is to check the water quality – ammonia, waste, and food might have piled up making the water toxic and unpleasant be in. If everything with the water is in order, then bring your fish to the vet as it might be suffering from parasite infestation. 

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