signs of too much oxygen in a fish tank

Can You Have Too Much Oxygen in A Fish Tank?

Angelfish require oxygen to breathe. Getting the right o2 levels inside the tank isn’t as simple as you might think. If the levels are too low or high, your angelfish can die.

Angelfish need around 8 PPM of dissolved oxygen to breathe. Too much oxygen can cause gas bubble disease, which can be lethal. The main indication that o2 levels are too high is too many bubbles in the tank. Low oxygen levels are more likely and are caused by not enough plants, too many fish, poor-quality substrate, and a lack of filtration. Suffocating fish will gasp at the water’s surface, stop swimming, and lose their appetite. 

When the tank’s oxygen levels aren’t right, owners must act quickly to prevent the fish from suffocating. Preventative measures, such as getting the right-sized tank, are essential for avoiding dangerous oxygen levels.

Do Angelfish Need Oxygen?

Angelfish don’t breathe in the same way as humans, but oxygen allows them to live. Therefore, oxygen is just as essential for their survival.

An angelfish’s heart has two chambers. The heart pumps blood to the gills, picking up oxygen and releasing carbon dioxide. The blood flows to the organs and tissues before returning to the heart. Therefore, oxygen keeps the respiratory process moving along safely.

Similarly, the tank needs oxygen to fuel the beneficial bacteria that break down oxygenate waste and remove harmful chemicals from the water.

Plants inside the tank also need oxygen to stay alive. If they don’t get enough o2, they decompose, raising ammonia and nitrites to harmful levels.

As described by the U.S. Geological Survey, angelfish consume oxygen that’s dissolved in the water through their gills, so the tank must be well oxygenated to keep the fish alive.

How Much Oxygen Do Angelfish Need?

While the exact oxygen levels vary between fish species, angelfish do well with 8 PPM of dissolved oxygen in the tank. When more oxygen in the water, more fish will stay alive. However, too much or too little oxygen can cause health problems.

According to the Florida Department of Agriculture and Consumer Services, the amount of oxygen that water can hold depends on its temperature, salinity, and atmospheric pressure.

While air pumps, bubbles, and oxygen diffusers help to add oxygen to the tank, angelfish don’t need them to survive. Instead, oxygen enters through the tank in two ways:

  • Surface agitation
  • Plant photosynthesis

Surface agitation oxygenates the water, promoting gas exchange. It increases the rate at which oxygen dissolves in the water and the rate at which carbon dioxide is released from the water. The benefit of surface agitation is that it allows more fish in the tank.

With plant photosynthesis, plants inside the tank use light energy to convert carbon dioxide and water into glucose. The by-produce is then released as oxygen, which fish breathe into the body.

However, angelfish do need a filter. Water filters remove unwanted chemicals from the water, such as ammonia and nitrites. It also agitates the surface water, providing an oxygenation bay.

does too much oxygen kill fish?

Does Too Much Oxygen Kill Fish?

Too much o2 in the fish tank can be deadly. It can cause gas bubble disease, which is brought on when angelfish are exposed to water oversaturated with oxygen.

It occurs when the total pressure of gasses that have dissolved into the water is higher than the ambient atmospheric pressure.

Affected fish develop small bubbles in the eyes and skin. Sometimes, the bubbles occur in the angelfish’s organs. The bubbles eventually become bigger, causing floating problems and ultimately death.

Also, when the disease transforms into air embolism, it blocks the lungs and blood vessels, leading to a slow and painful death.

Just like too much oxygen, a lack of it can quickly kill fish, too. Angelfish die within 12 hours if placed in an aquarium without a filter. Overcrowding and low water quality speed up the process of death.

When there’s not enough oxygen present inside the tank, angelfish suffocate and die. Similarly, when the temperature increases to above 32 °C, oxygen reduces to dangerous levels and kills the aquarium’s fish.

A dissolved oxygen meter can help you measure the oxygen in your angelfish tank. They’re not cheap and require regular servicing, but they’re accurate and can help prevent dangerous oxygen levels.

Signs of Too Much Oxygen In A Fish Tank

Too much oxygen in a tank is very unlikely. While gas bubble disease results from high oxygen levels, it’s more commonly caused by too much nitrogen.

As long as you’re using a stand aquarium setup and are maintaining adequate tank husbandry, you shouldn’t have an issue with too much oxygen. That being said, it can happen.

If your tank appears to bubble or fizzle like carbonated soda, it’s likely caused by high levels of oxygen.

Similarly, strong currents inside the tank can also be a problem. Not only can this risk excess oxygen forming, but angelfish prefer quiet, slow-moving waters. If the current is too strong, angelfish will become stressed and struggle to breathe.

As a result, keep the aeration inside the tank to a safe minimum to ensure the fish are comfortable and that you’re not risking the o2 levels getting too high.

If you suspect high oxygen levels, the only way to know for sure is to test the water and apply the appropriate methods to fix them.

How To Decrease Your Tank’s Oxygen Levels

When the oxygen levels are too high, you’ll need to lower them to safe levels. It’s relatively rare that the oxygen levels inside a tank would be too high, but if it happens, you’ll need to be able to spot the signs so that you can correct the levels.

As a result, it’s possible to lower your aquarium’s oxygen levels through the following ways:

Raise The Water’s Temperature

Cold water holds more dissolved oxygen than warm water. If your tank’s oxygen levels are too high, it could be because the water is too cold.

You must keep an angelfish’s aquarium between 78° and 84° F. Angelfish prefer warmer temperatures, so anything between these figures should please the fish and maintain oxygen levels at a stable level.

Keep monitoring the temperature to ensure it’s not dropping unexpectedly. If so, there’s a problem with the tank that needs fixing.

Remove Excess Plants

If adding plants increases the tank’s oxygen levels, removing excess foliage should help to reduce them. Overstocking a fish tank with plants looks aesthetically pleasing and provides plenty of hiding spots, but it can cause an overload of oxygen that makes fish unwell.

If this is the case with your tank, take out some of the plants. While they’re unlikely to do much damage, plants can be hard to maintain and die off quickly if they’re not cared for. Consequently, decaying plants may cause your tank’s oxygen and ammonia levels to rise to dangerous levels.

Remove Unnecessary Aeration Devices

Not all tanks require an aeration device to produce oxygen. For angelfish, surface water agitation is usually enough to give them all the o2 they need.

As a result, if your tank uses an aeration device it doesn’t need, you might be saturating the tank with oxygen, causing it to spike to dangerous levels.

The tank must be able to produce surface agitation. For many, a simple HOB filter is enough. Not only does it provide surface disturbance, but it moves oxygen to the bottom of the tank, increasing its concentration.

Remove excessive filters and monitor your fish to see if it improves.

Signs of Not Enough Oxygen in A Fish Tank

Unfortunately, it’s hard to tell when there’s not enough oxygen in the fish tank until fish become affected by it.

Increasing the levels should improve the problem, but owners must adopt good aquarium maintenance and monitor oxygen levels to prevent a lack of o2 in the tank. A lack of oxygen is caused by:

  • Lack of aeration
  • Poor water quality
  • Stress

If you notice your angelfish displaying the following signs, they might not be getting enough oxygen:

Gasping for Air

Angelfish that gasp at their tank’s surface are suffering from a lack of dissolved oxygen in the tank. This is serious, as the fish are in survival mode and are fighting to stay alive.  

Poor water quality, ammonia, and nitrites are leading causes of gasping, as these harmful chemicals take the oxygen out of the water. They also interfere with the fish’s gill function, preventing angelfish from being able to breathe in oxygen effectively.

If you have bubble filters, the angelfish will gravitate towards them in an attempt to find oxygen. When your fish are gasping at the surface, the situation is severe, and you’ll need to act fast.

Moving Less

Without oxygen to fuel them, angelfish become lethargic and their energy levels drop. They may stop swimming or float close to the tank’s surface. If they are still able to swim, they appear imbalanced and uncoordinated.

When this happens, the water’s quality has likely become compromised due to the factors causing a lack of oxygen. Angelfish are at risk of ammonia and nitrite poisoning if they’re not suffocated by the lack of o2 first.

Loss of Appetite

When there’s not enough oxygen in your angelfish’s tank, they struggle to breathe, let alone eat. A lack of dissolved oxygen in the tank reduces an angelfish’s appetite – they’re also physically unable to eat.

When angelfish stop eating, they become unwell. Without the right nutrients to sustain them, angelfish will quickly lose weight. In the worst cases, starvation leads to death.

A tell-tale sign that angelfish aren’t eating is uneaten food rotting at the bottom of the tank. If you notice this, not only do you need to deal with the insufficient oxygen levels, but you’ll need to clean out the tank of decaying matter to prevent harmful chemicals from forming in the water.

Labored Breathing

Angelfish that struggle to breathe will rapidly open and close their gills to find dissolved oxygen.

Healthy fish should breathe steadily. If a fish has to work too hard to breathe, something’s wrong – and it’s most likely the oxygen levels. To get your fish’s breathing back to normal, fix the tank’s conditions and monitor them to see if their breathing improves.

too much o2 in fish tank

How To Increase Oxygen Levels

When there’s a lack of oxygen in the tank, you must work quickly to increase o2 levels before the fish die. Without enough oxygen, fish will quickly suffocate, and you’ll lose your entire tank. Even the plants will die, so you’ll need to start again with stocking the aquarium. These are some of the best ways to increase your tank’s oxygen levels:

Add Plants

Adding plants to the aquarium helps to boost oxygen levels naturally. Plants also provide valuable hiding spaces that angelfish can use to escape from territorial fish.

However, when adding plants, you also need to add light to allow photosynthesis to take place. Make sure you account for the tank’s depth. If the plants are in constant darkness, the oxygen supply will quickly deplete.

Similarly, always clean out dead or dying plants and replace them with live ones to keep the oxygen levels topped up. This will also reduce the risk of harmful ammonia and nitrites forming.

Provide Proper Substrate

The right substrate should provide plants with enough nutrients to grow and develop strong roots. This means they’re more likely to live longer and provide oxygen more efficiently.

Fine gravel, small stones, or sand are all good-quality substrates that are suitable to use inside an angelfish aquarium. Dirt or loam soil provides a breeding ground for harmful bacteria, which can kill the plants. These materials should be avoided.

Ensure your chosen substrate comes with essential nutrients for plant growth. You can even add plant food to help the plants inside the tank grow.

Increase Aquarium Surface Area

When tanks have a larger surface area, there’s more oxygen. As a result, it’s essential that before purchasing a tank, you consider the shape and water capacity in order to provide enough oxygen for your angelfish.

If your tank is too small to provide all the oxygen your angelfish need, it’s a good time to get something bigger before problems arise.

Increase Surface Agitation

As surface agitation is one of the main ways angelfish get their oxygen, increasing the amount of water movement in the tank will help provide enough o2. You can do this with the following devices:

  • Surface bubbler. This releases streams of bubbles and oxygen.
  • HOB (hang on back) filter. You hang it on the back of the tank and it releases water into the aquarium at the surface.
  • Powerhead. This creates more water flow.
  • Wavemaker. This creates waves that agitate the water’s surface.
  • Spray bars and sprinklers. Both gentle add water into the aquarium

You only need to choose one of these devices, but each one should give your tank’s oxygen levels a boost.

Decrease The Number of Fish

An overstocked tank means there’s less oxygen to go around, resulting in angelfish needing to compete for it. Overstocked tanks cause several problems, including:

  • Increase in harmful chemicals
  • The risk of under and overfeeding
  • Aggression
  • Depressed fish

Therefore, it’s essential that you don’t add too many fish to your tank to both preserve the oxygen levels and keep your angelfish happy and healthy.

Monitoring the oxygen levels inside your angelfish tank is the best way to ensure everything is as it should be. Even the smallest oxygen rises or drops can be fatal, so observe your fish’s behavior for any noticeable changes, as this can show you when something’s wrong.