What Size Aquarium Does My Oscar Need? (Probably bigger than you think!)

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Oscars are large, powerful fish that grow to anywhere between 12” and 14” long. They need a tank which not only gives them enough room to swim around in, but also enough water volume that they don’t foul it quicker than the filter can clean in. I recommend a MINIMUM of 55 gallons for one oscar, but a 75 gallon is much better. If you are hoping to keep more than 1 oscar, you should look at a 125 or a 155 for a trio.

I first started keeping Oscars about 30 years ago. Since then, many have passed through my fish room. I have kept almost every color strain on the market. Currently, I have a 180 gallon (680 liters) aquarium with a trio of Lemon Oscars. It is an aquarium full of movement, color, and character.

What Size Aquarium Does My Oscar Need?

Oscar aquarium size is one of the most hotly debated topics on the internet today. Spend enough time reading posts on forums or Facebook and you will be told the minimum size aquarium for an Oscar is anything from 20 gallons to 200 gallons.

I have kept many Oscars over the years, and I know from first-hand experience how big Oscars get and how quickly they get there. I would say the absolute minimum size aquarium for a single Oscar is a 55 gallon (210 liters) aquarium. A 75 gallon (285 litres) is even better!

What Makes A Good Oscar Tank?

OK, so you have a tank which is a suitable size, what else does an oscar need, apart from the water! An Oscar really doesn’t care too much for decorations and they will destroy plants in no time at all. In fact, whatever you put in the tank, there is a good chance your oscar is going to move around to where he wants it to be.

All of my oscar tanks start off the same way. I place a sheet of egg crate (also known as a lighting diffuser) on the bottom. This helps protect the glass if the oscar does give the rocks a good shove. Next, I add the largest rocks I can, whilst still giving the Oscar space to swim around.

Notice I put the rocks in before the gravel. That way, as the rocks are already on the bottom, they can’t topple over if Oscar decides to dig under them. Next comes a decent layer of gravel. Any substrate will do. Your oscar won’t care.

Don’t put too much effort into landscaping it. Oscars are like little bulldozers. They will push the substrate wherever they want it to go. The only other thing we might add is a large terracotta pot or two, just to provide a cave-like hiding place. Most Oscars won’t use them, but they are there if they do want to get away from their tank mates.

If you are yet to buy your substrate, why not have a look at my article How Much Substrate Does My Aquarium Need?


What Filter Does My Oscar Need?

I am a big fan of canister filters for my Oscars. Canister filters such as the Fluval 406 typically turn over large volumes of water every hour which increases the chances of getting your fish waste and uneaten food up and out of the water.

Hang on the back filters can also work well, but a large tank may need two or three with one at either end and one in the middle. The filter media inside your canister filter isn’t too important for the oscar tank, just make sure it has plenty of mechanical filtration (such as layers, of course, medium and fine sponge) to catch all the debris floating in the water column.

I recently wrote an article about Fluval canister filters which is titled Are Fluval Filters Good?

Will My Oscar Tank Need A Heater?

The answer to that is, probably. If you live somewhere where the air temperature is in the high 70’s or low 80 all year round, then you won’t need an aquarium heater. Otherwise, you definitely will. I use the LED heaters from Fluval. They are easy to adjust, have a digital display on the front confirming the current temperature and they have a heater guard built-in, which makes it much harder for your oscar to break them.

Does My Oscar Tank Need A Light?

Your Oscar itself doesn’t care if the tank has a light or not. The only reason we have lights on our Oscar tanks is so we as aquarists can see them better and enjoy them more. A low-cost LED fitting from Amazon will do the trick fine.

You won’t be growing any plants in the tank, and the lower the light, the less on an algae problem you’ll have.

What Else Does My Tank Need?

There are some additional sundries you may need, but most of them aren’t essential. I use a magnetic glass scrapper to make maintenance easier and a python for changing water.

I always have a couple of buckets kicking around and a good water conditioner such as Seachem Prime to remove chlorine from the water when we carry out water changes.

In Conclusion

When it comes to Oscar tanks, size really does matter. You will find plenty of articles saying it is fine to put an Oscar in a 40-gallon tank. A 40 is just too small. A 55 gives more swimming space but crucially more water volume and a 75 is better still.

If you want to keep multiple Oscars, the tank size must reflect that. Take the time to do your research before buying and don’t make the classic mistake of saying I’ll get the small tank now and upgrade it in a few months.

Oscars grow at a rate of knots, putting on up to an inch a month. Before you know it he’ll be 10” plus and there will always be a reason you haven’t bought the bigger tank yet. Start off with the right size tank and your oscar will reward you with years of pleasure. They are a true wet pet.

About the Author

I’ve been keeping, breeding, and showing tropical fish for nearly 30 years. Over that time I’ve done it all! I’ve had great success and I’ve made some really foolish mistakes (like the time I bought an Asain Walking Catfish). Read more…
Richard James

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