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Koi Betta Fish: A Complete Care Guide

Koi Betta Fish: A Complete Care Guide

Numerous novice hobbyists are confused about a koi betta fish. Is it a common marbled betta? Or a normal betta fish? Well, to answer these questions and more, we have written this informative article just for you.

What is a koi betta fish? This is a selectively bred marbled betta. It displays a color pattern similar to a koi fish. Their koi-like color portions and patterns gave rise to their name. Usually having black, yellow, red or orange color patches, they are quite expensive compared to the marbled betta. 

You can buy Koi Betta Online on Amazon.

In the following sections, we will have a detailed look at all aspects of this precious fish.

Quick facts

  • Temperature: 25-27°C
  • Adult size: 3 inches
  • PH level: 6.0-8.0
  • Lifespan: 3 years
  • Diet: Carnivore
  • Species: Bettas
  • Tank size: 2.5+ gallon
  • Care level: Easy

Koi Betta Care

Naturally, these bettas originate from small streams and rice paddies in Southeast Asia. This includes Thailand, Vietnam, and Indonesia to mention but a few. The weather conditions in this region are usually warm and due to consistent rainfall, the water is of high quality.

As such the koi betta should be kept in warm water of at least 22-26°C. Additionally, the temperature should remain constant and the water should also be of high quality. This means that, you should constantly check water conditions – pH, ammonia, and nitrite levels – at least once a week.

You should also change the water twice a month to keep it clean. The koi betta prefers a densely planted aquarium with plenty of hiding and resting spots. The live plants also act as a source of food.

Water should be soft with a neutral to slightly acidic pH – 6.0 to 8.0. Additionally, the water movement should be kept at a minimum to mimic their natural habitat. However, if the koi are in a large tank, you should provide a spot where the water is slow moving.

They also do well in water with a low oxygen saturation. This is because they have a respiratory organ that allows them to breathe air from the surface. As such, they should have access to the surface of the water.

You should never keep two males in one tank. Why? Koi betta males are aggressive towards each other and therefore you must only ever keep one male per aquarium.

What is the lifespan of a koi betta fish? If they are kept in optimal water conditions and fed appropriately, they can live for almost 3 years.

How big do koi betta get? Koi betta reach a maximum adult size of 3 inches.

Do koi bettas change color? They do naturally change color, but only very gradually when compared to other bettas. In fact, how they look at 3 months old might be the same as how they look at 1 year old. However, a sudden change of color might be a sign of an underlying ailment or sudden change in water conditions.

Are koi bettas aggressive? Male koi bettas are aggressive towards other males. Additionally, they are aggressive towards females during breeding when the females try to get closer to the bubble nest. Also, they might show aggression towards certain tank mates.

Can koi betta live together? Yes. You should keep at least five females (sororities) with one betta male. Never keep two koi betta males together. For successful sororities consider tank size, planned coverage, and the personality of the fish.

How long do koi bettas live? They have a maximum lifespan of 3 years.

Feeding and nutrition

In the wild, koi betta fish predominantly feed on insects and insect larvae. This explains why they have an upturned mouth, well suited to snatching insects on the water surface. Furthermore, since they are carnivores, their digestive system is geared to digest meaty food.

In captivity, you should feed them with live insects and larvae. However, they will easily adapt to eating frozen and freeze dried foods. If you choose to feed them with pellets and flakes, supplement the diet with live or frozen foods.

How often should you feed koi betta fish?

Mature fish can be fed once or twice a day, while it is recommended that young fry are fed three times a day.

How much do you feed?

The belly of koi betta naturally stretches and this can be dangerous with foods that expand in the stomach such as dried foods. The right amount of food should make the stomach assume a round shape. However, you should keep in mind that mature females have a rounded stomach anyway, since they carry eggs.

My koi betta fish is not eating?

They are picky eaters and they do prefer live foods to dried and frozen ones. As such, if you feed them too many pellets and flakes, you should supplement the pellets with live insects or frozen brine shrimps and blood worms. Alternatively, you can opt for sinking rather than floating foods. If this does not do the trick, try giving them live foods.

How can I tell if I’ve overfed my fish?

The most obvious signs of overfeeding are excess waste in the aquarium, and the fish not eating. Ensure you feed them with the right amount of food – once or twice a day. This way you’ll reduce the chances of overfeeding.

How do I tell if my fish is bloated?

If the belly does not return to its normal size in the next feeding schedule, then your fish buddy is bloated. Do not feed it until the bloating has gone down. Alternatively, you can feed it with high fiber food that will assist digestion.

Koi Betta Fish

Koi Betta Breeding

Any hobbyist can breed koi betta fish successfully in a 10 gallon tank. Choose fish that are under a year old as they are ideal for breeding since they are still very fertile. The urge to breed decreases with age. The breeding pair should be conditioned before breeding.

Ensure the water pH is about 7.0 and the temperature is 27°C or above. The male betta will build a bubble nest where the eggs will be kept. You should provide a safe hiding spot for the female as the male becomes aggressive during courtship.

Once they start spawning, the male will circle around the female and show off his intense coloration. The female will start expelling her eggs as the male fertilizes them. The male will then scoop the eggs and spit them into the bubble nest.

After this, remove the female since the male becomes aggressive as it tends to the eggs. After the young ones hatch, they’ll consume the yolk sack. Remove the male betta after 2 days since it might feed on the young ones.

Tank Set up

Before you can set up the tank for your koi betta, let’s look at what you will need.

What tank size should you pick?

Most hobbyists keep koi betta fish in tiny bowls or 1 gallon tanks. While this is fine, the koi will lead a dull life and eventually become ill as it ages.

We bet you don’t want your fish to be bored!  So, what should you do? Purchase a 5+ gallon tank (link to amazon) to establish the nitrogen cycle that will lead to a healthy and colorful koi betta fish.

Do koi betta fish need a filter?

They do need a filter to keep the water clean, therefore mitigating the buildup of toxic materials that will eventually inhibit their immune system. However, purchase a gentle filter since koi betta cannot swim in turbulent waters. Check this Filter on Amazon.

We would recommend an adjustable filter that facilitates the creation of optimal water currents.

Do koi betta fish need a heater?

Of course, they do need a heater. They come from warm Southeast Asian tropical regions such as Indonesia. Here, the temperatures are constantly warm. As such, you will need to purchase a submersible water heater to keep the water temperature between 25 and 27°C. I recommend you check this heater on Amazon, it’s one of my favorites!

If the temperature is too high, you risk speeding up the aging process. If the temperature is too low, this increases the risk of infections. The most ideal heater should come with a thermostat for convenient monitoring.

For your peace of mind, never install a heater in a tank that is smaller than 5 gallons.

Do koi betta fish need decorations and plants?

Koi fish come from streams that have thick vegetation. Therefore, you should provide plenty of plants and hiding spots such as caves which provide shelter from aggressors. They also enjoy sleeping and resting on wide leaves.

Provide smooth decorations that won’t hurt your fish buddies. For artificial plants, we’d recommend silk rather than plastic ones.

Do koi betta fish need lighting?

Koi betta fish need lighting conditions very similar to your own. They have a daily schedule – night (sleep) and day (wake up). Therefore, you should switch off the lights when going to bed. Alternatively, you can buy aquarium LED lights that come with automatic timers.

How to set up for your Koi Betta fish

Purchase the right tank

You can purchase anything from a 2.5 gallon tank. However, we’d recommend at least a 5 gallon tank. You should also purchase a heater to keep the temperature constant and a vacuum to clean the tank.

Choose the right location

The tank shouldn’t be too close to the window because it can get too hot in summer or too cold in winter. Additionally, keep it away from heat radiating objects since it shouldn’t be too warm. A flat and stable surface is recommended to place the tank on.

Add substrate: Carefully add thoroughly cleaned substrate into the tank. Gravel is the most ideal substrate for koi betta fish.

Add water: After the substrate has settled in place, add water into the tank.

Install the heater and filter: Once switched on, they should bring the water to the right conditions.

Add décor: It’s time to add those live and artificial plants. Additionally, add caves and tunnels into the tank.

Test the water: Once everything is up and running, test the water to ensure everything is in order. Check pH levels, temperature and other conditions such as how clean the water is.

Introduce your fish: Finally, introduce your fish buddies and provide them with some food. At first, they might not eat but as they get used to the new tank, they’ll get their groove back.

Is my Koi Betta fish male or female?

Distinguishing between a male and a female koi betta fish is a daunting task even for pet store owners. Additionally, it is hard to tell the gender of the betta fish when they are still young since sexual dimorphism becomes apparent in maturity – 2-3 months of age.

So how can you tell a male from a female?

  • The ventral fins of males are naturally wider, longer and bulky while in females they are thinner but can be of the same length.
  • Females have shorter fins than males. However, this depends on the tail type. Once you know the tail type, you can accurately distinguish between both.
  • Mature females have an egg spot which resembles a white lump. It is found between the head and ventral fins. However, young females do not have this spot.
  • Males have a bulkier body and their head is curved while the females have a streamlined body.
  • The males are brightly colored compared to females. This explains why most hobbyists prefer males to females.
  • Males have more flowing fins than females.

A female betta will darken her colors in response to male’s mating advances. However, during breeding, they will display intense coloration.

Compatible Tank Mates

Never keep two males in one tank since they’ll fight to the death because of their aggressive and territorial nature. Koi betta fish can actually thrive on their own without tank mates. However, if you want to add a tank mate, it should have the following traits:

  • Peaceful
  • Dull colored
  • Short-finned
  • Tropical fish

The fish might mistake a long finned fish for another betta and a fight might ensue. Additionally, it’s best to introduce the koi betta fish into an established tank. This will mitigate instances where it feels as if his territory is being invaded.

Corydora Catfish

  • Temperature: 22-26°C
  • Size: 2.5 inches
  • Lifespan: 5 years
  • Tank size: 10+ gallon
  • How many: 5+

They are peaceful and timid schooling fish. They thrive in groups of 5-6. They are bottom feeders hence will rarely come into contact with koi betta fish.

Bristlenose Pleco

  • Temperature: 15-17°C
  • Size: 5”
  • Lifespan: 5 years
  • Tank size: 25+ gallon
  • How many: 1

They are small, peaceful bottom dwellers that are liked for their cleaning capabilities. They are hardy fish and can thrive in tough conditions.

Kuhli Loach

  • Temperature: 24-30°C
  • Size: 4 inches
  • Lifespan: 10 years
  • Tank size: 20+ gallon
  • How many: 5+

They are peaceful bottom-dwellers that scavenge whatever they find on the substrate. When keeping them together with koi bettas, ensure the substrate is sand rather than gravel. Gravel tends to hurt their bellies.


  • Temperature: 22-30°C
  • Size: 2.5 inches
  • Lifespan: 1 year
  • Tank size: 5+ gallon

How many: Any number. However, you should not introduce a lot since they breed rapidly.

You can add any variety of snails to a koi betta fish tank. They feed on all the waste materials they find in the substrate. Snails are bottom-dwellers and therefore rarely come into contact with the betta fish.

Most Common Koi Betta Fish Behaviors?


This is an aggressive display used to intimidate an intruder. The gills cover-up, the fins become erect and the fish might swim from side to side. While flaring is viewed as a defense mechanism it is also a way of relaxation. Therefore moderate flaring is healthy.

Bubble nesting

When the male koi betta fish makes bubble nests, it shows that it is extremely healthy. It also shows that he is ready to breed and has already taken his territory. In fact, female bettas can also build bubble nests.

Jumping out of the tank

This is a natural instinct that is common in all betta species. It is due to the nature of their habitat. They originate from rice paddies and streams in Asia. During dry seasons, the fish jump, hoping to land in a body of water.

However, jumping in a tank can indicate some mistakes in the aquarium. For example, the aquarium might be too small, the water might be toxic, the fish hungry, or the water too warm or cold.

Glass surfing

Naturally, koi betta fish swim around just to keep their territories safe. However, excessive swimming near the sides of the tank indicates that the fish is stressed and could possibly jump out of the tank. On the other hand, if he surfs when you approach, he may be expecting you to feed him.

Related Questions

Where can I buy koi betta fish?

You can purchase this expensive betta fish from local pet stores. However, sometimes they are in small supply, in which case we’d suggest sourcing them from reputable online pet stores.

Do koi betta fish recognize their owners?

Yes, they do. Whenever you walk towards the tank the betta will surf near the glass, waiting for you to feed it.

Koi betta fish are ideal to keep in an indoor aquarium. Their brightly colored patterns will definitely jazz up your tank. Ensure you keep them in optimal water conditions and introduce the right tank mates for them to thrive.

Kathy Reid

Wednesday 29th of January 2020

Hi! I have a koi betta, he is still young. He what you call a teenager and very aggressive. He doesn't like anything in his tank. I made a mistake by buying a algae eater and he attacked it, I had to rescue the little guy. He only likes his live plants and 1 plastic plant and he won't eat pellets or dried blood worms only frozen blood worms or brine shrimp and he loves peas.

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