Fish Laying On Bottom Of Tank? 13 Reasons Why

Oct 31, 2021

betta fish lying on bottom

Credits: PINKE (Creative Commons license)

Fish have their own little ways to communicate how they’re feeling. Unfortunately, most of the time, we don’t understand these subtle cues. When I first dabbled in this hobby, I had a fish lying on the bottom of the tank most of the time. I thought it was just out of habit but later realized it was due to ammonia poisoning. By the time I figured it out, the fish was already dead – a day late, a dollar short, I guess. 

Don’t worry yet – turns out there are a plethora of reasons behind this – some good, some bad. I’ll tell you all about it so you can deduce the right cause. 

Why Is My Fish Laying On Bottom Of Tank?

Most often, a fish lying on the bottom of a tank shouldn’t be alarming. It’s pretty normal behavior – even more so if your fish is a bottom-dweller like a catfish. Fish also sleep and rest at the base. However, if your fish spends most of the time at the bottom, this is a red flag. Your fish may be diseased and stressed. 

If you think this is the case, quarantine the fish as soon as possible until you find out the right reason and treat it accordingly. 

Here are all possible reasons why your fish is lying on the bottom of the tank:

  • The tank is too hot
  • The water is cold 
  • Your fish has white spot disease 
  • Your fish has swim bladder disease 
  • Your fish hasn’t adapted to a new environment 
  • Ammonia poisoning 
  • Nitrate poisoning 
  • Too much current
  • The tank is too small
  • Your fish is stressed
  • Your fish is resting
  • Your fish is sleeping 
  • Your fish is a bottom dweller 

The Tank Is Too Hot

Getting the water parameters right is the most essential thing in the fishkeeping hobby. Fish are highly susceptible to temperature shocks. Depending on the species, the water’s temperature should fall between 75-80°F (24-27°C). 

The thing with warm water is that it releases oxygen a lot faster than cool water. Your fish may be able to tolerate the warmth, but they’ll quickly suffocate from the lack of oxygen. So, the fish will move to the bottom of the tank, where the water is colder and hence more oxygenated. 

A hot tank will also increase your fish’s metabolism – leading to more excrement and ammonia-producing bacteria. This will eventually deplete the tank’s oxygen levels. 

If you think a hot tank is a problem, don’t rush and immediately lower the temperature. Remember, they’re prone to temperature shocks. This should be done gradually. You can do this with an air conditioner or a fan. And to infuse some oxygen into the water, use an air pump. 

Here’s a link to Tetra Whisper Air Pump that boasts thousands of raving reviews on Amazon! These are available in different capacities for tanks ranging from 10-100 gallons. 

If the temperature isn’t lowered and water is not oxygenated in time, chances are your fish will die of suffocation. Don’t use ice cubes or ice packs to lower the temperature. This won’t just shock your fish but also demolish the good bacteria colonies. 

And if you think lighting is the culprit here, switch to LED lights that emit little to no heat. 

The Water Is Cold

Coldwater is equally dangerous for fish as hot water, if not more. As reptiles and amphibians, fish are cold-blooded animals. They maintain optimum body temperature by absorbing heat from their environment. So, we cannot stress enough how important it is to get the temperature right. 

Coldwater slows the fish’s metabolism. But, unfortunately, it also restrains the oxygen intake process. The combination of these two events makes the fish tired and lethargic. And naturally, the fish will swim to the bottom of the tank and rest there. 

If you think cold water is the problem, you should raise the temperature gradually, so the fish isn’t shocked. 

You can use an in-tank heater or a light source to slowly raise the temperature. We recommend doing just one thing at a time to avoid a sudden temperature rise. 

Your Fish Has White Spot Disease (Ick)

White spot disease, also called ick, is among the most dreaded infections in the fishkeeping hobby. Ick is super contagious – and what’s worse is it doesn’t even need a host to transmit to other fish. It’s caused by a parasite called ichthyophthirius multifiliis and manifests as tiny white spots dotted across the body. 

Ich makes the fish itchy, who then tries to soothe it by rubbing its body against substrate and decors. And this is the reason your fish is hanging out at the bottom more often. 

According to the University of Florida, this is the most prevalent reason behind a fish lying on the bottom of the tank. 

It’s super important to treat the disease as early as possible. Otherwise, all the fish in your tank will be food for worms. 

Your fish is prone to ick if the temperature isn’t right, the fish is stressed, the immune system is weakened, and the diet is wrong. Besides white spots and itching, other signs of ich are abnormal hiding behavior, loss of appetite, faded colors, and heavy breathing. 

If you believe the fish has contracted ich, increase the water’s temperature by a couple of degrees and use a chemical treatment simultaneously. 

Medicate the fish for 1-2 weeks, depending on the severity. 

Here’s a link to API’s Super Ick Cure Remedy that’s suitable for both freshwater and saltwater fish. 

You can also bathe the fish using a potassium permanganate solution. 

Here’s a video instruction on how to give fish a potassium permanganate bath safely:

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Your Fish Has Swim Bladder Disease

The swim bladder is filled with gas (usually oxygen) and functions as a ballast organ that helps fish maintain their balance without sinking or floating upward. And naturally, a fish suffering from swim bladder disease will lose the buoyancy and swim in strange patterns – often dropping to the bottom of the tank. 

The swim bladder can be narrowed due to digestive problems like overfeeding and constipation, as well as a physical injury or abnormality. 

Although the condition isn’t lethal, it will severely stress the fish and compromise its immunity. 

Besides distorted buoyancy, other common signs of swim bladder disease are a curved back, a distended belly, and loss of appetite. 

If you suspect it is triggered by a digestive problem, slightly increase the temperature and fast the fish for 3 days. Feed a cooked and skinned pea on the fourth day and continue to do so for a couple of days until the symptoms subside. 

If it’s due to an infection, you will have to treat it using a broad-spectrum antibiotic prescribed by the vet. 

And lastly, if it’s due to an internal injury or abnormality, the fish surgeon will partially remove the bladder or place a tiny stone on it to restore balance. 

Your Fish Hasn’t Adapted To New Environment 

All fish get stressed when being transferred to a new environment. Most likely, the water chemistry is quite significantly different than that of their previous home. 

The anxiety is even greater if the tank already has a proper hierarchy and pecking order in place. So, most new first fish act timidly in the first couple of days – staying alone and hiding whenever possible. 

If your tank lacks proper hiding places like caves and plants, the fish will swim to one corner at the bottom and stay there until it feels comfortable. 

If the tankmates are compatible, the new fish will slowly lose their inhibitions and explore the new home. 

So, if your new fish swims to the bottom and spends most of the time there, it’s expected behavior. But if it persists for long, you might want to look into other reasons. 

Ammonia Poisoning 

Ammonia is inevitably produced in a tank when the fish produces waste. And you probably already know that ammonia is lethal for fish. It will cause chemical burns in the gills and prove fatal if not treated in time. 

The signs of ammonia poisoning are reddish or purplish gills, red streaks across the body, lethargy, and lowered appetite. If proper intervention at the right time isn’t taken, the fish will die from internal hemorrhaging. 

The acceptable level of ammonia in a freshwater tank is less than 1 ppm (part per million). If the levels increase above this number, your fish becomes vulnerable to ammonia poisoning. This usually happens when you set up a new tank or when the tank is crowded. 

You have to be aware of the tank’s ammonia levels at all times. To maintain it, amp up your filtration game and perform weekly water changes. 

A fish suffering from ammonia poisoning can become sick quite seriously. And as you know, an unwell fish will lay at the bottom of the tank. 

Here’s a link to Seachem’s Ammonia Alert sensor that very accurately tracks ammonia levels continuously. It lasts me almost a year and costs very little.

And here’s the link to API’s AMMO-LOCK Ammonia detoxifier I use to completely eradicate ammonia in the tank. 

Nitrate Poisoning 

Consistent exposure to high nitrate levels causes the fish to lose its energy, become sick, and lie on the bottom of the tank. Nitrate is yet another compound produced by fish waste. Good bacteria present in a well-cycled tank will convert ammonia to nitrites. They will then break nitrites into nitrate. 

Although less harmful than ammonia and nitrite, nitrate can still inflict a good deal of damage. And even worse, nitrate is a slow killer. 

Nitrate poisoning is often accompanied by lack of appetite, faded colors, rapid gill movements, panting, and lethargy. 

On several websites, most aquarists shared that nitrate range between 20-40 ppm is ok to have in a freshwater tank. However, this dangerous myth originated from the fact that nitrate is less harmful than ammonia or nitrite. 

Actually, the nitrate level should never exceed 10 ppm. 

And even if the nitrate level in your tank is high, you shouldn’t drastically reduce it because that would be just as dangerous for your fish. 

Some ways to gradually reduce nitrate levels are:

  • Reducing feeding frequency 
  • Adding air stones 
  • Using filtration media that removes nitrate 
  • Little but multiple water changes 
  • Chemical intervention 

I use this API Freshwater Test Kit to measure nitrate levels in my tank and 4 other vital parameters. 

Too Much Current 

Fish like danios, gold barbs, yoyo loach, and rainbowfish prefer strong currents. On the other hand, fish like bettas like to live in water with low currents. 

For those who fall in the latter category, strong currents can seriously tire them out. After all, it takes plenty of energy to constantly move against a strong current. So, they often take some much-needed rest by lying at the bottom of the tank. 

To lower the water flow from the filter, attach a sponge filter. You can also direct the current towards decors and plants. Breaking up the current can significantly lower the flow throughout the tank. 

Tank Is Too Small 

Fishkeepers often underestimate a fish’s need for space and assume they can live just about everywhere. It’s even truer in the case of small fish like bettas and guppies, who are usually kept in the confines of a 2-gallon tank! 

When the tank doesn’t have enough space, the fish has nothing to do. There’s no room for exploration and exercise. So your fish will naturally lose interest in things quickly and just lay on the bottom to kill time. 

A bigger tank is always better than a small one. It is less temperamental and offers plenty of room. Add decorations like caves, plants, and driftwood in the tank to play up things. 

A small tank also there means greater territorial aggression among its residents. Sometimes, subdued and timid members have nothing left to do than quietly live at the bottom of the tank. 

Your Fish Is Stressed

Stress is the strongest and most common reason behind a fish acting erratically. Fish are highly intelligent and complex than we like to think. And all of the reasons that I mentioned above are stress-inducing factors for fish. 

A stressed fish often looks to hide and becomes reclusive. And what better place to go than the tank’s bottom, right? 

If you see your fish constantly lounging at the bottom, try to figure out what might be causing stress. It could be harassment from mean tankmates, wrong water parameters, incorrect diet, and so on. Honestly, there are so many possible reasons. 

What’s worse is a stressed fish’s immunity becomes compromised, inviting a wide range of diseases and infections. 

Experiment to relieve the fish’s stress until you get to the right reason. 

 Your Fish Is Resting 

A fish lying on the bottom of a tank isn’t always alarming. If you have ruled out all of the reasons stated above, it’s most likely that the fish is just getting some rest. A fish looking to relax often swims to the lower third of the tank and stays there. 

Observe the fish carefully. If the pelvic fins are still gently moving and the fish is breathing normally, it means the fish is just taking a moment to relax. 

This is often the case with older fish. An average aquarium fish’s lifespan is anywhere between 3-5 years. And towards the end of their life, they need a considerable amount of rest, just like us. 

Even healthy fish will take occasional breaks between active swimming sessions. So make sure to provide plenty of rocks and cave-like decorations where they can retreat in when tired. 

Unless you have raised the fish from the fry stage, it’s difficult to determine the age. Even if you got your fish only a month ago, it might already have spent a couple of years at the breeder’s. So, if the fish generally looks healthy but has slowed down a little, it’s most likely the fish is getting older. 

Your Fish Is Sleeping

Most fish have the same sleeping rhythm as us. They remain active in the daytime and rest at night. Interestingly, fish need around 8-12 hours of sleep per night. So, if your fish lays on the bottom at the same time every day or night, it’s most likely sleeping or napping. 

But since fish don’t have eyelids, it can be difficult to tell if they’re snoozing or not. So, here are some other signs to know if the fish is sleeping or not – the slow movement of tail and fins, gentle breathing, and upright resting position. Some fish, like bettas, sleep sideways. 

A fish deprived of sleep will often catch up on it during the daytime. 

Don’t forget to keep the light on a diurnal schedule. 8 to 10 hours of light per day will suffice. Leaving the lights on all the time is going to confuse and stress the fish, who will then resort to erratic behavior. 

Your Fish Is A Bottom Dweller 

My apologies if this one is a little too obvious, but yes, chances are that your fish is a bottom dweller or a bottom feeder. Some fish are naturally inclined to live at the base as part of their survival and hunting strategies. 

For instance, clown loaches lurk at the bottom to attack their natural prey, snails. Kuhli loaches aren’t just known to lie on the gravel but cover their entire wormlike bodies into it. Timid zebrafish like to hide among the plants at the base, whereas corydoras simply enjoy hanging out there with a friend or two and scavenging together. 

Here’s an interesting fact: If your fish’s mouth is located more to the bottom of his head, it is most likely a bottom feeder who will spend a considerable amount of time at the base. 

And here’s a shortlist of some bottom dwellers:

  • Chinese algae eaters 
  • Kuhli loaches 
  • Corydoras catfish
  • Otocinclus 
  • Plecstomus 
  • Synodontis catfish
  • Zebra loach 
  • Twig catfish
  • Bumblee goby
  • Siamese algae eater

Frequently Asked Questions 

Credits: Aaron Tabarejo (Creative Commons license)

Why Is My Oscar Fish Laying On Side At Bottom Of Tank?

Oscars are big fish, growing anywhere between 10-12 inches long. That’s why the most common reason behind an oscar laying on its side at the bottom is lack of space in the tank. However, other underlying causes like stress, wrong parameters, and aggression can also be the reasons. 

Why Is My Betta Fish Laying On Bottom Of Tank?

Betta fish have long, beautiful fins, but they don’t really have any other purpose besides being eye candy. So, they get tired quickly if the water current is too strong, forcing them to lay on the bottom. Besides this, stress, illness, and an inhospitable environment can also be the reasons. 

Why Is My Molly Fish Laying On Bottom Of Tank?

Mollies are tiny, peaceful fish. That’s why they can’t hold their own against dominant fish, and this is the reason why they retreat at the base of the tank. But foul water, cramped tank, and lack of space could be the likely reasons too. 

Final Words: Fish Laying On Bottom Of Tank?

We don’t understand a fish’s antics as much as we know our dogs and cats. However, fish have their own little, subtle ways of communicating how they are feeling. And laying on the base of the tank is definitely one of them. 

Don’t jump to a conclusion if this doesn’t happen often. Also, they are known to rest and sleep at the bottom. 

However, if this behavior doesn’t subside and you see your fish spending more time at the base than swimming, you should look into the matter deeply. 

The reasons could range from wrong temperature, toxic buildup, diseases like a swim bladder infection and ick, and stress. 

Don’t panic – but experiment with ways to relieve your fish until you get to the right cause. Happy fishkeeping!

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rohit gurung author at urbanfishkeeping

About Rohit Gurung

My never-ending love and fascination with Aquascaping started when I received a red-eared turtle for my 10th birthday.

Apart from researching and writing, I spend hours gazing at my 3 turtles. And yeah, I bask alongside them too.