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Oscar Fish Staying At The Bottom Of The Tank: 7 Easy Solutions

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As I saw my Oscar fish laying at the bottom of the tank, I knew I had a problem. My tank appears to be in good order, so what was causing this behavior? Luckily, as time passed, I learned why this was happening and how to deal with the issue.

Oscar fish tend to lay at the bottom of the tank due to stressful conditions, including abrupt water changes, disease, ammonia, and overcrowding. These will force Oscars to find rescue at the tank’s bottom. However, sometimes Oscars stay at the bottom merely because they are sleeping.

As we move forward, I will share seven tips that will help you, or your Oscar fish, cope with these stressful conditions or aid in overcoming them. Then, I will list a few signs that may indicate your Oscar is actually dying. These cases require your immediate response.

Also Read: Stress In Oscar Fish

Why Is My Oscar Laying On The Bottom Of The Tank?

Oscars are midwater fish. As such, if your Oscars have decided to spend all their time at the bottom, no one would blame you for panicking. Though, while this behavior is a sign of serious trouble in some Oscars, it is reasonably innocent in others, as you will soon see:

1. Personal Preference

Oscars are like people. They have different personalities. Some of them will lie at the bottom for no apparent reason. In fact, some aquarists expect all Oscars to do this from time to time. But, ultimately, this shouldn’t concern you. 

If your fish is healthy and your tank is well maintained, this habit shouldn’t worry you. However, some Oscars are just lazy. On a side note, these kinds of Oscars will act this way from the moment you buy them. So if your fish has just started acting this way, something else is wrong.

2. Your Oscar Is Sleeping

Like many fish, Oscars sleep. They will lie still at the bottom of the tank when you turn the lights off.[1] You can test this theory by stimulating the water whenever you find your Oscar at the bottom. If you tap the glass lightly or add food to the water, a sleeping Oscar will most likely respond. Sick or stressed Oscars, on the other hand, are just as likely to ignore your efforts.

3. Abrupt Water Changes

Oscars do not like change, and they may respond to sudden alterations in their environment by becoming less active. Where tanks are concerned, change may manifest in three forms:[2]

  • New Fish – If your Oscars were active in the tank at the store, but all they do is lie at the bottom of your home aquarium, they are not yet accustomed to their new surroundings. They may even hide depending on their temperament. You just have to give them time.
  • Parameters – Oscars will respond negatively to rapid and unexpected changes in parameters like pH, temperature, and hardness. This can happen in fish that were not properly acclimatized before you added them to a new tank, especially in cases where the parameters in the new tank differ from those in the old tank.
  • Water Change – You are supposed to change the water in your tank to keep it clean. However, if your water changes are too large, they may produce significant shifts in the aquarium, harming the Oscars in the process. The creatures are likely to react by lying at the bottom and becoming less active.

4. The Wrong Water Parameters

Elevated nitrate, nitrites, and ammonia may stress Oscars, forcing them to lay at the bottom of the tank. You should also check the temperature, pH, and hardness. The wrong parameters are sources of stress for your fish. In the second part of this article, I will show you how to do that.

5. Your Tank Is Too Small

Oscars are big fish that may grow by an inch every single month.[3] As such, if you bought your tank to match the size of a young Oscar, it may outgrow the aquarium before it reaches adulthood. Small and overcrowded tanks generate stress.

They are also challenging to maintain, mainly if messy fish like Oscars populate them. The accumulation of waste in a cramped tank can hurt your fish. It will become less active, spending its days at the bottom before it finally dies.

6. Your Oscar Is Sick

Oscars are vulnerable to various diseases. One of the most problematic is Ich. Because it causes white spots to appear all over the creature’s body, some Oscars spend a lot of time at the bottom because they want to rub their bodies against the substrate.

If your fish doesn’t have any symptoms that would traditionally point to Ich, Oscars are also susceptible to Hole in the Head Disease, Fin and Tail Rot, Popeye, and Dropsy, to mention but a few. A sick Oscar is more likely to lie still at the bottom of the tank.

7. The Wrong Temperature

A hot tank will force its inhabitants to run to the bottom. This is because warmer water holds less oxygen than colder water. If the water in your tank is too hot, Oscars will look for sanctuary at the bottom because the water in that section is not only cooler, but it has more oxygen.

Some Oscars may do the opposite. They may rush to the top to escape the oxygen-deficient levels below because the top layer has more oxygen. But don’t assume that the oxygen isn’t an issue simply because your Oscar isn’t gasping at the surface. Some Oscars prefer the bottom.

Also Read: Oscar Fish Temperature

8. Aggressive Companions

Poor quality water, toxins, rapid changes, and high temperatures are not the only sources of stress in fish. Oscars may also respond to conflicts in the tank by hiding at the bottom. The creatures are somewhat aggressive. They will fight each other as well as other species because of their territorial sensibilities.

Oscars that cannot compete favorably against larger and more violent fish are more likely to stay at the bottom of the tank, either because they want to stay away from their enemies or because they are stressed.

Also Read: 19 Great Oscar Fish Tank Mates

How To Treat Oscars That Lay At The Bottom?

Many Oscars lie at the bottom because they want to. But if yours is spending far too much time on the substrate and you have observed signs of ill-health in the creature, you can use the following steps to treat it:

1. Providing Enough Space

Start by giving your Oscar sufficient space in the tank. You need at least 75 gallons, especially if you want to house more than one fish.[4] Larger tanks are easier to maintain. They also allow Oscars to live stress-free lives. 

Because Oscars are so big, the more Oscars you have, the bigger the tank. For example, an aquarist with three Oscars requires roughly 200 gallons. If your current tank is too small, another option is to split your fish into several groups in different tanks.

Also Read: Oscar Fish Tank Size

2. Adjusting The Water Parameters

For Oscars, please maintain the appropriate pH (6.5 to 7.5), temperature (68 to 83 Degrees F), and hardness (5 to 20dKH).[5] It is also crucial that ammonia, nitrates, and nitrites are around 0 ppm.

For that purpose, I use the well-known API Aquarium Test Kit (link to Amazon). That is my favorite since it is highly cost-effective and easy to use. Moreover, it comes with a test strip that gives you a reading within moments.

Also Read: What Is The Best pH Level For Oscar Fish?

3. Conducting Proper Water Changes

Do not expose your Oscars to massive water changes. A 25-30 percent water change is sufficient each week. Also, try to be gentle while adding new water to the tank. If you have a strong filtration system, it will prevent conditions in the tank from deteriorating to a point where a significant water change is required.

If the concentration of toxins like ammonia, chlorine, and chloramine is too high, use a water conditioner, such as Seachem Prime (link to Amazon). If your Oscars are so stressed that they are lying still at the bottom of the tank, a significant water change designed to remove toxins will make things worse for the creatures.

Make sure you acclimatize them properly using the drip method before they join a new tank. Even more importantly, ensure that their new tank is properly cycled. Otherwise, significant water changes will be the least of your worries.

4. Adjusting The Lightning

The standard lighting in a conventional room is sufficient for most Oscars. They do not have any specific lighting requirements. But it would help if you avoided excessively bright lights. I also suggest giving them a maximum of 12 hours of light. Keeping the lights on for too long will agitate them.

Also Read: Do Oscar Fish Need Light?

5. Placing A Few Hiding Spots

Use plants and decorations to create hiding places for Oscars, especially in aquariums with larger and more aggressive fish. With Oscars, fake plants are the best option because the fish tend to destroy real foliage.

But if you prefer real plants, you can go with varieties such as Java fern, Anubias, and Java Moss. These plants are low-maintenance, and they do not require much of your time. Remember that you should not overcrowd the tank with plants because Oscar fish like to swim briskly.

Also Read: Why Is My Oscar Fish Hiding?

6. Dealing With Diseases

If your Oscar is sick, you should find an appropriate treatment. Many fish spend a lot of time at the bottom because they have swim bladder disease, which affects the organ that fish use to maintain their balance in the water. This should be your initial focus.

Check for symptoms of swim bladder disease such as loss of appetite and erratic swimming behavior. If you have good reasons to assume that the sickness is present, you can apply the necessary therapies. That includes raising the temperature by a few degrees and keeping the Oscar on a fast for 48 hours.[6] 

If swim bladder disease isn’t the problem, look for other symptoms. As was mentioned above, Ich produces white spots. You can treat it with products such as Copper Sulfate and Malachite Green.[7]

Hole in the Head, on the other hand, is associated with holes and sores, loss of appetite, and white sores around the eyes. Aquarists use a drug called Flagyl to fight it.

Fin rot destroys the fins and produces lethargy and loss of appetite. You can use tetracycline or chloramphenicol to treat it.

If you can aid your Oscar in its recovery, it will become more active. It will also leave the bottom of the tank. Bear in mind that in many cases, maintaining a clean tank with suitable parameters is enough to heal the sick Oscar.

Also Read: 17 Oscar Fish Diseases

7. Providing Enough Food

Give your Oscars a healthy diet that includes live fish (if possible), insects, worms, vegetables, flakes, and wafers, to mention but a few.[8] However, try not to overfeed them. As a rule of thumb, give them the amount of food they can finish within two minutes.

You should also pay close attention to their tankmates. Because they are so large, your Oscars may eat all the other fish in the tank that can fit in their mouths. But that isn’t your only problem. More energetic fish may compete for food with the Oscars, consuming all the items you have added to the tank before the Oscars can feed.

When you consider the potential that Oscars have for aggression, you can probably understand why some people think that Oscars should only be kept with other Oscars. If you want a more diverse tank, Oscars can live with Green Terrors, Blue Acara, Chocolate Cichlids, Arowanas, Plecos, etc.[9]

Also Read: How To Feed Oscar Fish

How Do I Know If My Oscar Fish Is Dying?

These signs indicate that your Oscar fish is dying:

  1. The fish will cut back on the amount of food they eat or stop eating altogether.
  2. Your Oscars will move sluggishly or lay still at the bottom of the tank.
  3. Dying Oscars will open and close their mouths rapidly due to respiratory distress.
  4. The colors of a dying Oscar may fade significantly.
  5. Your Oscar will become bloated.

If you notice these signs in your Oscar fish, you should isolate the fish and consult a veterinarian. If the cause of the symptoms is a disease, you can use a cure recommended by your vet to save the fish. But if the creature is already dying, there may be nothing you can do to save it.

Also Read: Why Is My Oscar Fish Not Moving?


The fact that your Oscar is spending a lot of time at the bottom of the tank is not necessarily a sign that it is dying. It can also signify that the fish is bored, stressed, or simply wants to hide at the bottom. The fish may also be ill or in search of food.

If your Oscar has other symptoms, such as loss of appetite, damaged fins, or respiratory distress, you should try to treat the creature. If you suspect it is sick, isolate the fish and look for a vet immediately.