Over the years, I have witnessed my guppies staying at the top of the tank in different ways. Surprisingly, each case had its own reasons and ways to fix it.
This and the fact that it is such a common topic made me write this article. Below is a table that collects the most common scenarios and the possible underlying causes:
| Guppies stay close to the surface | Oxygen deficiencies, toxins, and cold temperatures |
| New guppies swimming at the top | Stress due to a recent change in their environment |
| Guppy floating at the top | Most commonly a swim bladder disease |
| Guppy staying at the top by the filter | The water current is too strong |
| Female guppy stays at the top | She is possibly pregnant and about to give birth |
| Guppies swimming at the top third of the tank | A normal swimming behavior |
As we move forward, I will help you identify each case and show you the steps you can take to help your guppy. So, without further ado, let’s dive into it.
Also Read: Stress In Guppy Fish
Why Are My Guppies Staying At The Top Of The Tank?
If your guppies swim at the top of the tank right by the surface and stay there most of the time, there are three main reasons you need to look for, which are:
1. Oxygen Deficiency
If there isn’t enough oxygen dissolved in your aquarium, your guppies, as well as other fish, will prefer to swim at the top.
Like humans, fish need oxygen to survive. They used their gills to extract it from the water.
Naturally, the area near the surface contains more oxygen because it has direct contact with the air.
And if the lower sections don’t hold enough oxygen, your guppies will choose to swim at the top, where they can breathe more comfortably.
Here are some signs suggesting your tank is low on oxygen:
- Most of the fish in your tank swim at the top.
- There is no agitation or bubbles in your tank.
- Your guppies breathe fast and move their mouths rapidly.
- The guppies seem to be producing more bubbles than usual.
Solution:
Fixing this issue is quite simple. All you need is to create agitation, allowing the oxygen to dissolve more easily.
As a rule of thumb, the more bubbles you have in your tank, the more oxygen it will hold. That is because bubbles break the surface tension.
You can simply get it done by installing the Hygger Aquarium Air Stone (Amazon link). I personally picked this one because it is incredibly quiet.
But to be honest, most airstones will do the job just fine. The only important thing is to locate it in such a way that the bubbles can reach the surface.
If you place the airstone under dense foliage or decorations, the bubbles will get trapped there and lose their purpose.
2. Toxins (Ammonia, Nitrite, And Nitrate)
High toxins, including ammonia, nitrite, and even nitrate, can compromise your guppies’ breathing.
And just like with a lack of oxygen, if your fish have trouble breathing, they will swim to the top where there is more oxygen.
You typically see this in under-maintained tanks with a lot of debris and leftovers. You can also find this issue in overpopulated tanks with too many fish.
This problem mimics a lack of oxygen, even though there is enough of it. This is because your fish cannot use it properly for breathing, as their gills are damaged.
These are usually associated with the problem:
- Ammonia and nitrite are above 0 ppm.
- Nitrate is above 40 ppm.
- You may see red streaks on your guppy’s gills (ammonia burns).
- Debris and residue can be seen on your plants, decorations, and substrate.
- Algae bloom in your tank (as they feed on these toxins).
- Some guppies will develop black patches or gradually lose their color.
- Your guppies consistently shake and swim erratically.
- Some guppies will die for no apparent reason.
Solutions:
- Perform a significant water change (about 50 percent).
- Siphon the substrate using an aquarium vacuum device (at least once a week).
- Consider getting the Seachem Prime Conditioner (link to Amazon), a well-known product that detoxifies ammonia and nitrite instantly.
- Look for dead fish and remove them immediately.
- Pull out leftovers and debris stuck on your plants and decorations.
- Consider diluting your aquarium population.
As for the last part, I highly recommend following the inch-per-gallon rule. This means that for every inch of fish length, you will need at least one gallon of water.
For example, if you have a 2-inch guppy, it will need at least two gallons. If you have five of them you will need ten gallons, etc.
3. Cold Water
If the water in your tank is too cold for your guppies, they will naturally swim to the top, where the water is relatively warmer.
Just like air, cold water tends to move to the bottom, while warm water will rise to the top. This can happen in tanks with a malfunctioning heater.
These signs indicate that you have a temperature issue in your tank:
- The temperature at the bottom is below 72° F (22° C).
- The temperature at the top is above 72° F (22° C).
- Some of your fish consistently swim near the heater.
- You have recently got a larger tank but kept the old heater.
- Your guppies will swim up and down vertically.
If that is the case in your tank, you probably need a better heater. When purchasing a new one, make sure the wattage is adjusted to your tank’s size.
It is worth noting that guppies can live in cold water, at temperatures as low as 60° F (15° C).[1] However, this will stress them and endanger their health in the long run.
Where Do Guppies Swim In The Tank?
Guppies are considered top dwellers. They may hang at the bottom or behind plants and decorations when stressed, but mostly, they prefer the top.
For this reason, it can be perfectly normal for your guppies to stay at the top of the tank. However, there is a difference between the upper third and the surface of the tank.
Guppies can naturally swim in the top third of the tank, even if everything is fine with their environment. That is totally fine.
Yet, they shouldn’t hang too close to the surface the entire time. This is a behavior of distressed fish that are suffering.
You should also look for other signs besides the part in which your guppies swim, such as lethargic behavior, loss of appetite, rapid breathing, red streaks, etc.
These will indicate that your guppies are stressed, and are probably swimming the way they are because they are not comfortable with their surroundings.
Why Are My New Guppies Swimming At The Top?
This case is a bit different as the guppies you grow are new to their tank.
In the classic scenario, you’ll see the new guppies swimming at the top, while the rest of the fish stay at the bottom.
That usually happens because your guppies are stressed and are not accustomed to their new environment.
This behavior is expected to resolve within a few days. Obviously, you should still rule out the causes mentioned earlier, just to be safe.
Why Is My Guppy Floating At The Top Of The Tank?
A guppy fish that is floating at the top is entirely different than a guppy that chooses to swim at the top.
Guppies that float are usually sick and appear to be upside down or sideways. In many cases, they will also seem fat and bloated.
These are classic symptoms of swim bladder disease. In short, fish use this gas-filled organ to control their buoyancy and stabilization.[2]
By controlling the amount of gas in this organ, fish can change their depth position without wasting energy on swimming.[3]
However, there are a few conditions that can prevent this organ from functioning properly:
- Poor water quality (stress-induced).
- Infections (parasites and bacteria inflame the swim bladder).[4]
- Extended belly situations (constipation, air gulping, fatty organs, kidney cysts).[5]
These are just a few of the many causes of a swim bladder disorder. If you suspect that your guppy suffers from this condition, you can take the following steps:
- Let the fish fast for three days.
- Increase the temperature to 78-80° F (25-26° C) and keep it there during treatment.
- Feed your guppy a cooked and skinned pea on the 4th day.
- Make a partial water change and clean the tank thoroughly.
- Apply an aquarium salt (typically 1 tablespoon for every 5 gallons of water).
- Consult a vet for a wide-spectrum antibiotic treatment.
Why Is My Guppy Staying By The Filter?
Many times guppies will choose to stay at the top of the tank, particularly by the filter. Obviously, that can be due to any of the reasons mentioned above.
However, this behavior may also indicate that the current in your tank is too strong for your guppies.
Guppies are pretty gentle and require medium to low currents. So, in order to avoid strong ones, they may choose a dead spot, which is right next to the filter outlet.
Yet, before replacing your filter and getting a new one, you should rule out the other reasons mentioned earlier, including the temperature, toxins, and oxygen.
Why Is My Female Guppy Staying At The Top Of The Tank?
If only one female guppy hangs at the top, and you are sure it is actually a female, this could be a sign that the fish is pregnant and ready to give birth.
Female guppies choose to do this because the upper parts are usually calmer and considered a safe place to give birth.
Here you can find an article in which I talked about this phenomenon in detail. You can also check this article, where I explained how to tell if your guppy is pregnant.
Also Read: Why Do Guppies Lose Their Color?
Conclusions
Guppies are considered top dwellers, which is why swimming at the top can be a normal behavior. Nevertheless, even the top area has different sections.
If your guppies hang very close to the surface, you should consider reasons like oxygen deficiency and high toxins. Sometimes even cold temperatures make them do that.
In case your guppies are new to their tank, it could be that they are just stressed due to a rapid change in their environment. Let them adjust and see if it improves spontaneously.
A single guppy that floats at the top is an entirely different case. In this situation, you should consider a swim bladder disorder and follow the steps mentioned above.