Why Do Guppies Stay an the top of the Tank?

Do you feel that all your guppies do is stay in the corner of the tank for hours on end? 

If so, then without long intros- let me teach you why that happens and how to fix it.

TL;DR Summary

Why Do Your Guppies Stay At The Top Of The Tank?

What Causes it?

The main reason why your guppies stay at the top of the tank is a lack of oxygen. That happens when the water is dirty, the tank is overcrowded or the filter isn’t injecting enough oxygen into the tank.

How To Fix It

To fix it, test your water and make sure it’s within levels. Change the water if necessary. Then, you may need to increase the flow of your filter as it’s responsible for oxygen injection. Lastly, you can just install an air stone in the tank instead. 

"Because There's No Oxygen"

On Why Your Guppies Stay At The Corner Of The Tank

How To Spot A Lack In Oxygen

The #1 culprit to why your guppies stay at the corner of the tank is a lack of oxygen. 

You can tell your fish are experiencing a lack of oxygen by spotting any of the following signs:

  • Gasping and clustering at the surface
  • Rapid gill movement
  • Lethargy and/or loss of appetite
  • Resting near air stones or filter
  • Change in coloration
  • Excessive mucus production
  • Visible stress behaviors
Pro Tip

You can use an oxygen test kit to measure the oxygen levels in your tank to confirm the presence of oxygen deficiency.

Why Does Your Tank Lack Oxygen


Overcrowding happens when you have more than 1 inch of fish per gallon of water.

If your guppies have tank mates, like shrimp or snails those should also be taken into account. 

Another thing most beginners forget about is plants. If half of your tank is taken up by plants- they guppies are essentially living in 5 gallons of water.

High Water Temps

Warm water holds less dissolved oxygen than cooler water.

If the tank’s temperature is too high, the oxygen solubility decreases, making it harder for fish to extract sufficient oxygen from the water.

You may want to double-check your water temp with a second, external thermometer. Your water temp should be between 78-82F.

No Water Flow or Surface Area

Inadequate water surface agitation, caused by insufficient filtration or surface disturbances, can hinder oxygen exchange at the water’s surface, reducing the availability of oxygen for fish to breathe.

Stagnant water or dead spots within the tank can lead to localized low-oxygen zones. Fish may avoid these areas, causing them to congregate near the surface or in corners.

How To Fix Low Dissolved Oxygen

Air Stones And Air Pumps

Air stones connected to air pumps are excellent tools for increasing oxygen exchange.

These devices create a stream of bubbles that rise to the surface, promoting aeration. Place the air stone at the bottom of your tank to maximize oxygen distribution.

air stone omitting bubbles in a fish tank

The only thing with air stones is that they have 2 shortfalls:


They can be a little loud, especially if the tank is in your bedroom or office. 

A swimming dead zone.

Guppies will most likely not be able to swim through the constant flow of bubbles. Also, if food finds its way into the path- it’ll become a part of the dead zone. Also, If the tank is small but the “bubble zone” is too large you may be creating an overcrowding problem- because guppies won’t be able to use that space.

Adjusting Your Filter

Your aquarium filter can do more than just remove impurities; it can also enhance aeration.

If you have a hang-on back filter, or your filter came as part of the tank kit, then it will have a pump built in.

The way the pump works is by creating a current inside the tank that infuses it with oxygen. It also helps to achieve surface agitation- which is key for oxygen dissolvement. 

Live Aquarium Plants

Plants are awesome.

While some people think they are a pain their benefits outweigh the cons. 

Plants release oxygen into the water as they photosynthesize- which helps create more dissolved oxygen in the fish tank.

Here are a few more of the benefits plants offer:

  • Natural Filtration: Live plants help remove excess nutrients like ammonia, nitrates, and phosphates from the water, which can be harmful to fish if present in high concentrations. They act as natural water purifiers by absorbing and utilizing these substances.
  • CO2 Regulation: Live plants help regulate carbon dioxide (CO2) levels in the aquarium. They consume CO2 during photosynthesis and release oxygen, which benefits both the plants and the fish and helps control the pH in the water.
Pro Tip

Be mindful of floating plants like duckweed. If your tank is covered in duckweed you may not have a surface for surface agitation- hence creating an oxygen problem. 

Change The Water And It's Temp

Dirty water isn’t your friend- and it is too hot it might be just another reason why your guppies are staying at the top of the tank. 

Clean your water regularly- about once a week. Change about 20-25 percent of it on a regular schedule and make sure to test it periodically to monitor it.


Hot water has less room for oxygen in it. Maybe you bumped your water up for a sick or pregnant guppy- or maybe the thermometer is skewing just a little. To troubleshoot- simply use an external thermometer.


Your Guppies are staying at the top of the tank most likely because of a lack of oxygen in the tank. 

The reasons why your tank lacks oxygen can be:

  • The water is too hot
  • Tank is overcrowded
  • There’s not enough surface area agitation
  • There’s not enough water flow

To fix it, you can:

  • Install an air stone
  • Increase the flow of your filter
  • Lower your water temp to 78, or check your heater
  • Create more surface area by removing floating plants

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