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How Many Oscar Fish Can You Have In A 125 Gallon Tank? Facts & FAQs

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By Lindsey Stanton

tiger stripe oscar fish

Oscar fish are some of the most popular aquarium fish around. Their fairly large size and bright colorations make for quite an impressive fish. They are however known for being quite aggressive and territorial. You might be wondering if you can keep a few of these wonderful fish together.

So, how many Oscars in a 125-gallon tank can you keep? An Oscar fish needs between 55 and 75 gallons of tank space to be happy, with each additional Oscar requiring an additional 30 gallons. Therefore, you could house 2 Oscars in a 125-gallon tank.

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How Many Oscars Should I Get?

Oscar fish are a species of cichlid, and as a whole, these fish actually do quite well when kept on their own. In fact, these can be quite territorial and aggressive fish, which is why most people do keep them alone.

However, when provided with enough room, you can keep multiple Oscar fish together. Most people have no problems keeping 2 or 3 of them in the same tank, although they may get into little skirmishes every now and again.

oscar fish close up
Image Credit: madcat13shumbrat, Shutterstock

Minimum Tank Size for Oscar Fish

Oscar fish are quite large and can grow to around 10 inches in length, and they can be quite territorial too. Therefore, the minimum recommended tank size for a single Oscar fish is 55 gallons.

However, most people would recommend giving a single adult Oscar fish even more room, up to 75 gallons if possible.

Generally speaking, the more room you can give your fish the better, so we personally would aim for at least 60 gallons per Oscar fish.

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Oscar Fish Housing Requirements

Just like any other aquarium fish out there, Oscars do require a fairly specific tank setup to be happy and healthy.

Remember that these fish can be territorial and aggressive, and therefore, ensuring that they have plenty of space and an aquarium that mimics their natural environment is quite important.

Let’s take a closer look at what you need to know about Oscar fish housing requirements.

oscar fish in aquarium
Image Credit: Natalya Chumak, Shutterstock

Water Temperature

Oscar fish are used to living in fairly tropical waters, and therefore they do require you to keep the tank at a certain warmth.

The water temperature for an Oscar tank should be between 74 and 81 degrees Fahrenheit.

This is quite warm, so if you live in an area where the ambient air temperature does not keep the water warm enough, you will have to invest in a decent aquarium heater.

Water Hardness

Oscar fish like their water to be fairly soft to moderately soft, with a KH level between 5 and 20.

If you set your tank up properly, you really should not have to do anything in order to keep these fish happy in terms of the water hardness level.

That said, you may still want to test this from time to time, and if necessary, use water conditioners to make the water softer.

Water pH

Oscar fish in the wild live in fairly neutral waters when it comes to acidity. They do not do very well in high acidity or alkaline waters.

The water’s pH should be kept fairly neutral, with a pH level of between 6 and 8 being acceptable, although a perfectly neutral level of 7 is the ideal.

ph testing
Image Credit: M-Production, Shutterstock


Oscar fish can be quite messy. They eat a lot and they aren’t neat eaters, plus they do create a lot of waste as well.

Moreover, their tendency to dig for food can also dislodge debris in the substrate. This means that you do need a fairly strong filter for them.

For one, an Oscar fish tank filter should be able to handle at least 3 times the amount of water in the tank every hour.

So, if we are talking about a 125-gallon tank, your filter should be able to process at least 375 gallons per hour, although even more is better.

Also, because these fish tend to be rambunctious, you will want to consider getting an external canister filter that is relatively safe from harm.

Also, keep in mind that Oscars like fairly strong currents, so the flow rate of the filter can be kept fairly high.

Moreover, due to this, you will not need an air stone or air pump, as your filter should be able to provide more than enough oxygen for the tank.


In terms of lighting, you want to provide Oscar fish with a moderate amount of it.

A decent aquarium light, a basic one will do just fine here. It does not have to be anything overly special.


In the wild, Oscars tend to live in sandy waters, and therefore this is what you should be using as substrate.

High quality aquarium sand with a very fine grain size is ideal here. Soft sand that your Oscars can dig around in is what you need, and to make the aquarium look good with brightly colored Oscars, getting either white, yellow, or black aquarium sand is recommended.

About 2 to 3 inches of sand as substrate should be fine. Remember that it does need to be soft, because Oscars like to dig.

If you use something like gravel, Oscars are likely to injure themselves when digging.

aquarium plant aponogetone
Image Credit: Kuttelvaserova Stuchelova, Shutterstock


One of the most problematic aspects of keeping Oscar fish is that they are prolific diggers, they are curious, and they are boisterous.

They very often dig up and uproot plants, usually to find food, but also just because they can.

Therefore, when choosing plants for your Oscar fish tank, you do need to go with plants that are extremely hardy and resistant to being uprooted.

Most people would go for plants that can be tied to rocks or driftwood. Floating plants tend to be the safest option here, as there is no chance of them being uprooted.

Rocks & Decorations

Oscars do like to explore their tanks and they are used to living in natural environments with a fair amount of debris present on the waterbed.

Therefore, you will want to add a few basic rocks and pieces of driftwood to the mix, just to make them feel at home.

Tank Mates

The problem with Oscar fish is that they are aggressive and territorial, especially when kept in a tank. If you really want these feisty cichlids, it is best to keep your aquarium an Oscar only tank.

However, if you do feel the need to create a community fish tank, you need to get fish that are passive, so they will not challenge the Oscars, yet also large and hardy enough to defend themselves when need be.

Some examples of fish that meet these requirements include:

  • Severum Cichlids
  • Jack Dempseys
  • Jaguar Cichlids
  • Arowanas
  • Convict Cichlids
  • Silver Dollar fish
oscar fish in tank
Image By: madcat13shumbrat, Shutterstock

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What size tank do I need for 2 Oscars?

For 2 Oscar fish, you should have a tank that is between 100 – 125 gallons in size. A bigger tank is always better.

How many gallons does an Oscar fish need?

An Oscar fish needs 55 gallons of tank space at the least, although closer to 75 gallons is the ideal.

Can angel fish live with Oscars?

No, keeping Angel fish with Oscars is not a good idea. Angel fish will not be able to adequately defend themselves against Oscars.

Angel fish are likely to become stressed out if they are forced to live with Oscars.


Final Thoughts

The fact of the matter is that while Oscars are beautiful fish, they do need a lot of care and quite the specific tank setup.

They require regular tank maintenance, a very strong filter, specific plants, and they don’t make for great community fish either.

Feature Image Credit: Slowmotiongli, Shutterstock

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