Why Do Guppies Stay at the Top of the Tank?

Guppies are naturally top swimmers, and you’ll constantly see them near the water’s surface. However, it should be alarming when the fish overstays at the tank’s top. Sometimes it’s a sign of distress due to illnesses, low oxygen levels, or poor water quality.

Ideally, guppies prefer a water temperature of 72-78 degrees Fahrenheit and a Ph of 6.8 – 7.5. The water should be kept clean and well-oxygenated through regular water changes and using a filter. You also need to ensure that ammonia and nitrite levels in the tank are below 0.5 ppm.

Reasons guppies stay at the top of the tank

Fish are sometimes classified according to their swimming behaviors. Some fish are deep swimmers, while others prefer swimming at the top, like guppies.

However, guppies constantly staying at the top of the tank may signify the following:

1. Swim bladder illness

The swim bladder is a critical organ that enables the fish to have balance as they swim. It contains gases to maintain neutral buoyancy at the fish’s desired depth. If the organ is affected by a disease or an injury, the ability of the fish to swim appropriately will be compromised.

Affected fish are often found lying on the bottom of the tank or pond, or floating at the surface, explains Lawbart in the Fish Veterinary Journal, Swim Bladder & Buoyancy Disorders of Ornamental Fishes.

A guppy swimming upside down sometimes signifies a swim bladder problem or a physical injury on its fins. Poor water quality is commonly the main cause of these problems.

2. Lack of oxygen

Just like other animals, fish need oxygen for survival. However, oxygen concentrates more at the top of the tank than in the water at the bottom. This will typically force fish to move close to the water surface where they can tap the resource.

Various factors can cause a deficiency of oxygen in the tank, including the following:

  • Stagnant water – A tank with no filter or aeration pump will have stagnant water with little oxygen.
  • Warm water – Warm water also has little oxygen. If you live in a hot area or use a malfunctioning heater that could heat the water above the recommended temperature, oxygen levels may decline.
  • Overstocking – Too many guppies in a small tank can deplete the available oxygen leading to a shortage.

3. Poor water quality

Guppies, like other aquatic animals, have certain water parameter requirements. They require a temperature between 72 and 84°F and a Ph of 6.8 – 7.5. Changes in these parameters will make your guppy swim to the top for a conducive environment.

Ammonia, nitrate, and nitrite levels in the tank are also a major concern, as they are toxic to fish. Ammonia, in particular, is very toxic and forms when fish waste and leftovers decay in the water. High ammonia levels will harm the gills making it impossible for the fish to breathe.

4. Hunger and stress

Guppies know that they are fed from the top of the tank. Therefore when hungry, they will stay at the top of the tank in anticipation. You might also notice they swim toward the top each time you approach the tank. After feeding them, they will swim back to the bottom.

The guppies will also stay at the top of the tank when stressed. Keeping them with aggressive tank mates will make them move to the top of the tank for a peaceful environment.

New environments like a new tank, new tank mates, and a water change can also result in stress.

Guppies on top of tank

What to do

You should take the following measures if your guppy is constantly floating or swimming at the top of the tank.

Treat the swim bladder illness

If you suspect the guppy suffers from swim bladder disease, you must establish its cause for the best treatment. The disease is caused by several factors, including overeating, constipation, bacterial infection, and injuries from falling or hitting an object.

If the illness is caused by overeating or gulping air, you should withhold food for about three days. Increase the water temperature to 78 – 80°F during this fasting period.

From the fourth day, feed the fish with a cooked and skinned pea and continue for a few more days, then resume the normal feeding schedule. In the meantime, avoid feeding the guppy with floating flakes and pellets.

However, if the fish is injured or has an infection, you must consult a veterinarian to recommend the best treatment.  

Increase oxygen levels in the water

Low oxygen levels can cause ammonia poisoning and should be resolved immediately. Fish breathing fast, heavily, or rapidly is another common sign of low oxygen levels in the tank. You can increase oxygen levels in the tank by doing the following.

  • Use a filter to enable water movement, which helps in increasing oxygen levels.
  • Add live plants – Plants inhale carbon dioxide and exhale oxygen. The plants will inhale the carbon dioxide released by fish and, in return, will release oxygen into the water.
  • Clean the tank – Algae and accumulated waste will deplete oxygen as bacteria work to break down the excess organic matter.
  • Keep only the recommended number of guppies in the tank. You should relocate them or buy a bigger tank if you have more.

Improve the water quality

Improving the water parameters will provide a stress-free environment for your guppies. Keep the temperature at 72 – 84 degrees F and the Ph at 6.8 – 7.7. A regular water change will keep ammonia, nitrite, and nitrate levels at bay. Also, remove leftovers and fish waste to ensure the water is clean.

If you have a big tank, you can add a few mystery snails to help tackle the fish leftovers and algae menace. Mystery snails are peaceful and will coexist with guppies.

Feed your guppies regularly

Feeding the guppies regularly is important as it helps keep their immune systems strong. These fish can eat various foods, including frozen or live foods like brine shrimp and dried bloodworms. They also enjoy blanched vegetables such as spinach, lettuce, and zucchini.

Keep guppies with friendly tankmates such as neon tetras, mollies, and platies. Any hostile tank mates should be moved to a separate tank.

Final Thought

Guppies may naturally be drawn on top of the tank for enjoyment. Poor water parameters, insufficient oxygen, swim bladder illness, stress, and hunger can force guppies to move on top of the tank for survival.

It is important to investigate the guppies’ health and the tank conditions when the fish keeps floating or swimming on top of the tank.


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