is my angelfish stressed?

How To Tell if Angelfish Are Stressed

Angelfish can be easily stressed. They can be riled up by too much activity in the tank, overcrowding, or bad water conditions. Angelfish get stressed out when they don’t have enough hiding places and aren’t properly fed.

When angelfish are stressed, they tend to be more aggressive, swim at frantic speeds, and hide themselves away for long periods of time. They may also begin ‘surfing the glass,’ where they swim up and down against the tank for hours at a time. Angelfish that are growing ill from the stress may lose their appetite and change in appearance. They’ll be more prone to sicknesses, display fin rot, and have dimmer colors.

The best way to treat a stressed angelfish is to calm down its environment and return it to proper balance. This includes changing the water, checking the pH level, placing an oxygen pump in the tank, and treating any illnesses. If your angelfish is stressed by activity, then remove aggressive fish from the tank or reduce the population. All the fish may need to be given extra food, hiding spots, and have the water temperature adjusted.

Is My Angelfish Stressed?

Angelfish are capable of getting stressed and overwhelmed. Sure, they’re contained in a tank and don’t interact with the rest of your home. However, there are still annoyances, scary situations, and environmental changes that will leave your angelfish upset. The stressors that angelfish experience are placed in two categories:

  • Environmental stressors: These are problems caused by the way your tank is set up or how you adjusted the water parameters.
  • Social stressors: These are issues caused by other fish or the territory that’s established within the aquarium.

Both can be just as hard on your angelfish. If your tank occupants are exposed to even one stressor, they can grow ill over time. If they’re exposed to several, or a combination of both, that will snowball things more quickly.

The good news is, no matter the stressor, you can help smooth out the problem. You just need to identify the likely causes:

Improper Water Conditions

The water conditions of your tank are your angelfish’s entire world. According to ILAR Journal, if even one factor is slightly off, your angelfish may begin to:

  • Suffocate
  • Freeze or overheat
  • Struggle to process nutrients
  • Feel anxious or threatened
  • Struggle to recoup energy
  • Be unable to mate or reproduce

All of this will unbalance how your angelfish lives, interacts, and thrives in the tank. As such, it’s no wonder that you’ll spot angelfish in poor water quality growing ill or aggressive.

If you notice a sudden behavior change, angelfish gasping at the surface, or lethargy in the tank occupants, immediately conduct a water test. The main issues to look for will be:

  • A low or high pH level
  • Improper temperature
  • High nitrate or ammonia levels
  • Low oxygen levels can lead to stress
  • Imperfect salt levels in a saltwater tank

Problems With Other Fish

Angelfish are very social creatures, but are also territorial. This can make for a range of stressors if you population the tank carelessly. Angelfish easily become stressed if:

  • They are kept alone in a tank
  • They are only given a single companion and are unable to school
  • There are too many fish in the tank, which leads to overcrowding
  • The tank holds a bad combination of fish (such as aggressive species with docile ones, or large with small fish)

Angelfish should not be kept alone, as they will become restless and lonely. If they are only given a single companion, some angelfish will be fine, while others will still feel isolated.

On the flip side, angelfish require space to carve out their own territory. If they feel crowded by too many other fish, be they angels or another species, they can get defensive. As they try to protect their mate and zone, they can become overworked and stressed.

If angelfish are paired with incompatible species, this can lead to fighting. At the least, the angels will eat other fish that can fit into their mouths. They may also harass larger fish incessantly, killing them or exhausting themselves.

The same is true in reverse. Angelfish may get bullied by other fish and feel constantly threatened. The constant need to fight, run, or hide can wear down on their immune system and energy. Over time, the stress can be overwhelming.

signs of stress in angelfish


According to Aquaculture International, the diet has a direct impact on how resistant angelfish are to stress. When they’re given food high in vitamin C, E, and K, they can adapt to subpar conditions more effectively. 

Angelfish are omnivorous, but they require a high amount of protein in their diet. This means they need fish food, frozen food, live food, and freeze-dried food that leads toward a carnivorous diet. If you don’t provide the right amount of amino acids or protein, your fish will become stressed. The lack of nutrition will leave them lethargic, aggressive, and unbalanced.

In that vein, angelfish don’t react well to food shortages. If your other fish are driving them away at mealtime, the angels will grow stressed. Overcrowding will make them compete for food, and being housed with more aggressive fish can lead to starvation.


The temperature of the water plays a key role in the immune system of angelfish. They are known to tolerate water conditions slightly outside of their preferred zone.

However, if the difference is too wide, they may grow stressed and ill. For example, temperatures far above or below 78- 84 Fahrenheit can see their immune system weakening. This can lead to diseases, infections, and stress, which can lower their defenses even more.

Dirty Water

Even if your tank is perfectly set-up, and the population is balanced, the everyday waste can build up. If your filter has broken down without your notice, or you haven’t changed the water recently, the angelfish will grow stressed.

They will be forced to swim and breathe the filth, as well as tolerate the change in the chemical balance. Even forgetting to change the tank water for a week can lead to angelfish manifesting symptoms of stress.

Lack Of Aquarium Décor

Angelfish need space to explore, but that doesn’t mean keeping the tank empty. Hiding places should be placed throughout to ensure your angelfish have:

  • Places to set up territories
  • Places to hide from other fish
  • Objects that break the line of sight, so the angelfish don’t feel crowded
  • Items to lay eggs on or interact with

The substrate type is also important. For instance, the use of stone and gravel allows good bacteria to accumulate and maintain healthy nitrogen levels. Real plants can assist in stabilizing the CO2 and nitrogen levels.

Signs of Stress in Angelfish

Unlike in the wild, your angelfish cannot rely on the wide expanse of an ocean or river to give them distance from their stressors. Likewise, they have no control over what they can eat, what their environment is like, or how they can fend off the threat. Because of this, angelfish that are stressed in home aquariums tend to get sick in short order.

If left unattended, your angelfish may not recover. That makes it important to identify and resolve the problem as soon as you can. Keep an eye out for these angelfish stress symptoms that can warn you ahead of time:

Glass Surfing

Angelfish may revert to their natural instincts when stressed and try to escape. As they swim away, they will hit the glass and be forced to swim along it. This results in “glass surfing.” The angelfish will swim from the top to the bottom of the aquarium walls several times.

They may do this for hours, as if they’re trying to find a nook to slide through. Angelfish typically do this when they:

  • Feel overcrowded and want to get distance
  • Are trying to flee from a predator in their area, but are not being actively pursued
  • Are upset by a temperature imbalance and want to find a hotter or cooler area

Excessive Hiding

When new angelfish are introduced to the tank, it’s normal for them to hide in the initial few hours. This may even last for a day or two. For angelfish that are comfortable in the tank, they may hide as they recoup energy, feel threatened, or protect eggs.

However, it’s a bad sign if your angelfish hides almost constantly. If you do not see it emerge for several days, or it only comes out to feed, this is a symptom of stress.

Your angelfish is not simply winding down or taking a break from the other fish. Instead, it’s too afraid to emerge and feels constantly threatened by its environment. If only one fish is doing this, it could mean it is:

  • Sick
  • Injured
  • Being bullied
  • Feels overcrowded

If several fish do this, it indicates something is wrong with the water conditions. They may also be struggling with too much light exposure or activity from outside the tank.

Changes In Appearance

If the stress goes on long-term, your angelfish may physically show damage from the stress. This can include:

  • Dimmer colors that appear dull and lifeless
  • Stripes that fade away or appear faded in color
  • Scales that appear flaky or frail
  • Fins that seem ashy or thin

This will be especially prominent in angelfish that were bright and colorful before. This happens with angelfish that are stressed by:

  • Illness
  • Water conditions
  • Poor diets
  • Long-term harassment from other fish

If the angelfish have been attacked or bullied, they may also have physical injuries. These can include nipped fins, scrapes on their bodies, or even missing scales.

Fin Rotting

Fin rot sets in once your angelfish has contracted a bacterial infection. However, fish that are stressed and overtaxed will find their immune system is weakening. This makes them easy prey to fin rot. The infection may spread to the rest of the body, leaving raw patches that are both painful and unsightly.

While it is nasty and dangerous, fin rot is also very much preventable. The main cause of fin rot is poor water conditions. Polluted tanks lead to infections, which eventually cause the rotting of fins.

The stress resulting from this condition makes it harder for the angelfish to recover even after the water conditions have been corrected. Other causes may include:

  • Environmental changes
  • Fin nipping
  • Overcrowding

Loss Of Appetite

Angelfish are known for their big appetites. This is especially true when they are young and growing. If your angelfish refuses to eat, then it’s immediately worth your concern. They should be fed 2-3 times a day, and cannot survive more than 3 days without food.

If one meal is skipped, this can be fine, as long as it’s a rare occasion. Likewise, new fish that are introduced to the tank may avoid the first meal out of stress. However, once it calms down and acclimatizes to its new habitat, it should be hungry.

If the angelfish refuse more food, then it needs immediate help. The first step is to offer new meals, such as live food to hunt, frozen food that has been thawed, or protein-rich flakes. If the angelfish refuse this after a full day, then the loss of appetite might well be down to:

  • Poor environmental conditions
  • Bullying
  • Illness

You should assess the problem immediately and try to fix it. The longer your angelfish goes without food, the faster its health will deteriorate.

Constant Sickness

Your fish may become ill from bacterial or fungal issues in your tank. These can be treated with medication, but if the angelfish are in good health, they are unlikely to get sick often. If you have one angelfish that is constantly ill, or a batch that gets sick every few months, this is an issue.

Stress is likely the culprit. Stress can not only attract diseases, but also make existing diseases worse. Parasites have an easier time attacking the bodies of stressed-out fish. Your tank may be dealing with:

  • Overcrowding
  • pH imbalances
  • Wrong temperatures
  • An unbalanced diet

How To Treat Stressed Angelfish

When dealing with stressed-out angelfish, time is of the essence. Some issues can be resolved over the course of several weeks, while others give you a matter of days. If your angelfish are displaying any symptoms of stress, use these tactics to remedy the situation:

Remove Any Toxins From The Aquarium

Be sure to perform a 30% water change to your tank. This will help remove impurities and toxins from the water, and give your filter a chance to catch up. If your fish are already sick, this sudden change may be dangerous, so complete a 15% water change every 3 days. After that, perform a water change every week to ensure the tank is kept well balanced.

At this point, you should check that the filter is working properly. Clean it out, replace the filter media, and scrub down the parts thoroughly. Waste may build up in the little mechanisms, and if your tank is dealing with an infection, your filter may reintroduce it to the aquarium. Sanitizing it will prevent that.

If your filter can’t keep up, then you should look into buying a strong design. You can also purchase 3-stage filters that use mechanical, biological, and chemical media. This helps cover all your bases and offers cleaner water to your fish.

Adjust The Temperature

Improper temperatures, or fluctuations in temperature, can elevate the stress levels in angelfish. In extreme cases, it may also lead to shock or result in clots forming within your angelfish. Try to pick a temperature within their ideal range and stick with it.  

You can accomplish this by using a thermometer to check and monitor the conditions of the tank. If you need to change the water, try to adjust its temperature to match the tank water before pouring it in. If the conditions of your home are chilly, then you may need to invest in a tank heater to keep your angelfish well balanced.

how to treat stressed angelfish

Set The pH

The ideal pH for an angelfish ranges from 6.8 to 7.8. When the pH starts getting higher or lower than this, your angelfish may become stressed.

Although they can tolerate a broader range, it does put them at risk of aggression, lethargy, and illness. Use the aquarium monitoring system or pH testing strips to keep an eye on the pH level.

Provide Sufficient Hiding Spots

Try to incorporate more castles and rocks in the tank, so the angelfish have somewhere to hide. If you’ve just introduced new fish to the tank, try moving around these decorations to confuse territory lines.

That will keep established members of the tank from harassing newcomers. You can also add plants, driftwood, and other objects to mimic the natural habitat of an angelfish, so it feels at home.  

Eliminate Aggressive Fish

If you notice one of your angelfish harming or nibbling the other, then do not waste any time separating the two. A tank separator can be used to prevent the aggressive fish from fighting all the time.

You can also add decorations or move around the territory lines by rearranging objects in the tank. If this doesn’t work, then you may need to place the more aggressive fish in a tank of its own. If your aquarium is overcrowded, consider buying a larger tank or dividing the population into two different tanks.

Provide Sufficient Food

If your fish are competing for food, then you may need to offer more. Sprinkle some into the tank and wait for it to all be eaten. You can then offer more until the fish go away on their own. Any that’s leftover can be removed with a net.

It’s wise to sprinkle food across the length of the tank, rather than in one spot. This ensures all fish have an equal chance to feed, rather than hoarding into one spot and fighting.

If problems continue, then try to break the meals into several feedings. You can offer smaller portions 3-4 times a day until the fish learn they don’t need to compete.

Place An Oxygen Pump Inside The Aquarium

Without sufficient oxygen, your angelfish will struggle to breathe easily and comfortably. As a result, they might suffocate and die. The process of water mixing with oxygen is continuous, and carbon dioxide is constantly leaving the surface of the tank.

However, if you have fully covered the tank lid, the carbon dioxide will have nowhere to escape from. This will result in elevated carbon dioxide levels, which can prove lethal for your angelfish.

Air pumps are another effective way of ensuring that the tank water remains oxygen-rich. These air pumps consist of two inlets. One sucks in the air from the outside environment, while the other deposits that air inside the tank water. So, if you see signs of suffocation in your angelfish, waste no time inserting the pump.

Angelfish can be easily stressed, but always for a clear reason. If you notice the symptoms of stress, evaluate the state of your tank and see where you can make adjustments.