How to Increase Oxygen in an Aquarium

Low oxygen levels are not a problem in a clean, well-maintained, non-overcrowded aquarium. However, if you notice your fish gasping for air at the water's surface, it is a sign that something is surely wrong and needs quick attention. Most aquarium fish cannot survive for more than a day in water with very low oxygen levels. Let's find out the common signs of low oxygen, the causes, and the steps you can take to restore healthy oxygen levels in the aquarium.

Here is A Step-by-Step Guide on How to Set Up a Healthy Aquarium for Beginners.

How Much Oxygen Do Fish Need?

The amount of oxygen fish need depends on the species and where you live. Water at higher elevations contains much less oxygen than water at sea level. So, altitude can affect oxygen levels in the aquarium. The good news is that you usually don't need to measure oxygen unless you see a problem. If your fish are active, swimming normally, and not gasping at the surface, it means your aquarium has less oxygen. 

If you want to check the oxygen levels, you can use a dissolved oxygen (DO) meter. For most freshwater aquariums, a dissolved oxygen level of 8.3 ppm (parts per million) is considered safer and healthier for fish. 

What Are The Signs of Low Oxygen in A Fish Tank?

Low oxygen levels don't come with a warning alarm. The easiest way to identify a problem is to watch your fish's behavior. You can even confirm it by testing the water with a dissolved oxygen meter. Some of the common signs of low oxygen include: 

• Less Appetite: They can eat less or even ignore food altogether. 

• Less Activity: Fish become sluggish and spend more time resting. 

• Quick Gill Movement: Fish breathe faster when they try to take in more oxygen. 

• Gasping At The Surface: It is a serious warning sign that fish are struggling to get enough oxygen and need immediate attention. 

You need to keep in mind that some fish, such as bettas and labyrinth fish (gouramis), naturally gulp air at the surface. It is the normal behavior of these species and should not be mistaken for low oxygen levels. However, if most or all of the fish in your aquarium are gasping at the surface, you need to check the tank's oxygen levels and water quality.

What Are the Causes of Low Oxygen in a Fish Tank and How to Fix Them?

If your fish are gasping at the water's surface, you need to act quickly. Low oxygen can become dangerous quickly. You can start by changing about 50% of the tank water with fresh, dechlorinated water. Then increase water movement by adding an air pump, air stone, powerhead, or another filter. It helps increase oxygen levels when you fix the main cause of the problem. 

1. Overcrowding

If there are too many fish in the tank, they can use up the oxygen faster. An overcrowded aquarium also produces more waste, which further lowers oxygen levels. You need to move fish to another aquarium if the tank is overcrowded. Don't add too many fish than your tank can comfortably hold, and make sure your filter is powerful enough for your tank size. 

2. Too Many Live Plants or Algae

Live plants can produce a lot of oxygen during the day, but you need to use oxygen at night. If your tank has a lot of plants or algae, oxygen levels can drop after the lights go out. You need to keep the aquarium light on for about 8-10 hours each day. Cut off the plants, remove algae, and increase water movement using an air stone or filter, especially at night. 

Check out the difference between Live Plants vs Plastic Plants.

3. Poor Water Movement

You need to know that if the water is still, it can have less oxygen because there is very little movement for gas exchange. You need to check that your filter is working properly. To get started, you need to clean your clogged filter media. Then add an airstone, air pump, or spray bar. Make sure the filter outlet can create enough ripple on the water surface. 

4. Dirty Aquarium

Fish waste, leftover food, and dead plants can create extra waste in the tank. When bacteria break down waste, they can consume oxygen. You need to vacuum the gravel regularly, remove uneaten food, clean algae from the glass, and do regular water changes to keep the water clean. 

Wondering Why Your Aquarium Stinks? Know Why and How to Fix It.

5. High Water Temperature

Warm water cannot hold as much oxygen as cold water. If the aquarium gets too hot, oxygen levels can drop quickly. You need to lower the heater settings if necessary. Do a partial water change with slightly cold, dechlorinated water. You can even float a sealed bag of ice in the tank during emergencies. If needed, use a small fan to cool the water if needed. Don't make sudden temperature changes, as they can stress your fish. 

6. Aquarium Chemicals

Some fish medications and water treatment can reduce oxygen levels. You need to increase aeration when using medications. Make sure to keep the filter running unless the medication instructions say otherwise. Also, keep your fish under observation during treatment to see any signs of stress.

Check out 5 Common Mistakes to Avoid While Setting Up Your Aquarium. 

How To Add Oxygen To Your Fish Tank Manually?

If you don't have an air pump or other equipment, pour aquarium water back into the tank from a height to increase oxygen levels. When the water splashes out onto the surface, it creates the movement that helps more oxygen dissolve in the water. Here is how you can do it:

• Fill a clean cup, jug, or small container with water from your aquarium. 

• Hold the container a few inches above the tank and then pour the water back in. 

• Repeat the process various times to keep the water moving and improve oxygen exchange. 

There is not a fixed number of times you need to do it because every aquarium is different. You just need to watch your fish closely. If they continue gasping at the surface, repeat the process more frequently or use an additional method. It can include an air pump or partial water changes to increase oxygen levels.