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Guide to initial Setup for an Oscar Fish Tank

Written by ~Rush~. Posted in About Oscars

For those of you who are thinking about buying an Oscar fish, or for those of you who have impulsively bought an Oscar fish, this article will go over some basic pointers about setting up an aquarium for your new friend. Oscars are a serious commitment due to their longevity and adult size. Having the correct set up will make their transition from little wriggler to a big brute as seamless as possible.

This article serves as an overview of the different aspects of owning Oscars. For additional details we also recommend reviewing the New Oscar Owner Information Packet.

Oscar Tank Size:

There is plenty of debate about the minimum size for an Oscar Tank. I believe that the smallest aquarium an Oscar should be kept in is a 55 gallon (48x12x21 inches). This is not ideal, but it can be done. In a 55 gallon tank I can only recommend one Oscar with no tank mates and minimal decorations. This will also mean that you will be performing large frequent water changes to keep nitrates at a safe level for your Oscar. The average Oscar will grow to 12-14 inches in length. However there are some beasts that will grow up to 15 even 16 inches long. For these beasts I recommend a 75g tank. Let's not forget that bigger is better, and it seems that today there are more and more people providing 100 + gallon aquariums for their fishes. Don't be afraid to give them some extra space. It will be much appreciated.

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125 gallon tank. Black Tahitian Moon sand.

Oscar Tank Filtration:

I'm not going to get into the specifics of filtration and bioload here. Just know that Oscars are very messy fish and bring with them a large bioload. In most cases I recommend canister filters in conjunction with a HOB (Hang on Back) filter. That way if one filter goes down you have a back up. One thing is an absolute, unlike community fish that many new aquarist are familiar with, an Oscar Tank requires massive filtration with a focus on biofiltration. The more the better. If using HOB filters we recommend enough filtration to turn over the entire volume of the tank 10 times per hour. If using Canister Filters, our recommendation is enough filtration to turn over the tank volume four times per hour.

More about filtration here and here.

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Home made 110g tank. Plywood and acrylic face.

Oscar Tank Decorations:

In general, adult Oscars prefer swimming space. A tank that is packed full of decorations is no and ideal Oscar Tank. They like to be able to see potential threats coming so they can face them head on. Juvenile Oscars however, do enjoy some type of hiding spot so you may have to accommodate them as they grow. Using a large terracotta pot or a cave decoration can make a shy baby Oscar feel more comfortable. But as they mature they will become more aggressive and will not need or desire to hide as much.

Oscars are terribly clumsy fish. Couple that with the fact that we often keep them in small tanks and you've got a big bumbling brute in a jewelry store. Any decoration, rock, or driftwood with a sharp edge is a no-no. Oscars can be quite jumpy and if spooked they will run into whatever is in front of them. This can lead to scrapes, gashes, even damaged eyes. Use larger sized rounded rocks that cannot be moved, or driftwood that is sanded down. Most decorations you find at the pet store are safe as well as long as they are not pointed. Don't lean things upon each other. Stacking rocks is not recommended. Oscars are big powerful fish and can tip over such things that may lead to a disaster. Live plants can be tried with Oscars though as with most cichlids, they will most likely be uprooted frequently or just plain shredded to bits. IMO live plants are worth a shot because they can really add color and something else nice to look at. But don't expect them to survive or you will be disappointed more often than not. More about decorations here.


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55 gallon tank. Silica sand.

Oscar Tank Lighting:

For most Oscars, lighting is not significant. As long as you have a light it will work. Some though, prefer a more dim light than others. If you have an Oscar that shies away when you turn on the light or just seems more active when the lights are out then you may want to consider a different bulb or dimming the bulb you have. You can do this by wrapping the bulb in tinfoil and then poking holes through it allowing light through at the desired amount.

Oscar Tank Tops/ Lids:

Oscars are known jumpers. They have been looking 'up' for their food for centuries and even though the majority of Oscars we keep are far from their wild ancestors they still look to the surface for food. A lid or some kind of tank top is necessary to prevent your Oscar from jumping. If you bought a used tank and don't have a lid or a tank top you can fashion one out of some egg crate, or a cut piece of Plexiglas. Do Not train your oscar to jump out of the water for food. Too many Oscars leap out of their aquariums and either fall to their deaths or lie helpless on the dry floor. Unfortunately, you do not have to train some Oscars to do this, they just will. If you suspect that your Oscar is a jumper you need to weigh down the lid. Put some books or something heavy on the lids. If you are a neat freak and don't want a bunch of books or junk sitting on your fish tank, you can buy strips of velcro and use them to fasten your lids down nicely.

Substrate for an Oscar Tank:

Again, I won't go into the finer details about substrates or all of the available substrates for Oscars Tanks. The big debate between substrates is sand vs gravel. Either substrate will suffice for an Oscar. Just remember that Oscars like to dig. Fine sand can work its way up into a filter and ruin it. This is especially true if you have a large Oscar who likes to take a mouthful of sand and 'spit' it. Sometimes right into the filter intake. Be sure and use a pre-filter on the filter intake if you have sand or there is a good chance it will be damaged by the sand. More on Gravel vs. Sand.

You don't want too much substrate. Especially with gravel, uneaten food and debris will work its way down into the substrate so if I am using gravel I prefer a shallow substrate bed, 1 - 1.5 inches. Sand is more fine grained and doesn't allow debris and such to work into the bed (not as much anyway) so I like a deeper bed with sand 2 -2.5 inches. Others prefer a shallow sand bed. If left undisturbed, sand will allow gas build up from nitrogenous waste that is potentially dangerous. Sand needs to be stirred up so this gas cannot accumulate.

There are others still that prefer no substrate at all. Bare bottom tanks are becoming more popular due to the ease of maintenance. Some tanks with added water movement achieve a flow that doesn't even allow debris to settle. In most cases, the flow is directed toward the filter intakes so any debris caught in the flow will eventually be caught in the filter.

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125g tank. Natural gravel. (Same tank pictured above.)

Heaters in an Oscar Tank:

Heaters might not seem like a noteworthy point to hobbyists who keep small tetras or African cichlids. But for those who have kept large rowdy cichids you know heaters can be broken. Yes, that's right. Your Oscar can and likely will take a swing at your heater. A broken heater can cut your Oscar, over heat your tank, or in the worst scenario, electrocute and kill your Oscar. You want a heater that is shock resistant. Pretty much any heater that is glass is a bad idea for an Oscar tank. If you don't have the availability or already have a glass heater then you need to protect it somehow. You can make a heater guard out of some PVC piping cut in half (the long way) and attach some suction cups to it, or you can fashion a guard out of egg crate. Bottom line is that you want that heater protected from your big brute. The other point I want to make is that of heater malfunction. I personally have had two Marineland Stealth heaters somehow malfunction and over heat my aquarium. I lost several fish to this and I was severely disappointed. For this reason I cannot suggest these heaters. Stealths are known for being 'shatter proof' which is why I bought them. But after my experience I'll never own another. I currently have several other brands that I'm testing. A review of our current recommended heater can be found here.

Cycling Your Oscar Tank:

By Kmuda

Before setting up any aquarium, it is imperative you familiarize yourself with the concepts of the Nitrogen Cycle. The Nitrogen Cycle involves the establishment of the necessary bacteria to prevent a build up of toxic ammonia and nitrite which can be lethal to your Oscar. Unlike standard community fish, Oscars are designed by nature to live well in excess of a decade. If you purchase a tank, set it up, and immediately add your fish, your Oscar's chances of living its full life expectancy is greatly reduced, even if it survives the "cycle".

Tank Cycling involves much more than simply plugging everything up and letting it run for a few days. In order for the "cycle" to occur, there has to be a regular source of ammonia. For generations, a tank cycle was accomplished by using "throw away" fish such as goldfish. This practice involves setting up a tank, filling it with water, and dropping in some goldfish, which produce ammonia. Over a period of time bacteria become established that convert the ammonia to nitrite, then, once nitrite is present, bacteria become established to convert nitrite to nitrate (this is the Nitrogen Cycle.) Within the hobby, the process of establishing the nitrogen cycle in a new tank via the introduction of fish is called "Cycling with Fish". The problem is that very few fish that are used to establish a cycle will survive the process as both ammonia and nitrite are very toxic. Hence the term "Throw Away Fish".

Since it is unlikely you consider your Oscar a "Throw Away Fish", the only way for your Oscar to survive a cycle requires massive effort on your part. If you find yourself in this circumstance (we've all been there in the beginning, fish stores rarely give good advice), please create an account to access our forum and we will try and help you avoid disaster.

On this site, we consider the practice of "Cycling with Fish" to be inhuman. Instead, we practice a concept known as a "Fishless Cycle?". This process involves setting up a tank (including the filtration) and then artificially dosing with pure ammonia on a daily bases until the necessary bacteria become established. This process requires much less effort on your part (aside from locating pure ammonia, but if you google "Fishless Cycle" you will find plenty of advice on what the buy and where to buy it.)

Regardless of how you cycle a tank, it will take anywhere from two to eight weeks for a cycle to complete.

If you are interested in a better understanding of the bacteria that are so vital to the hobby of fish keeping, please read the below two articles, which are actually the foundation of a successful fish keeping philosophy.

Autotrophic Nitrifying Bacteria and Their Practical Application in a Freshwater Aquarium

Heterotrophic Bacteria and Their Practical Application in a Freshwater Aquarium

These few pointers should help you on your way to providing a safe and comfortable environment for your new pet. As always, if you have questions, please create an account, access our forum, and ask away. Here at Oscarfish.Com, our only motive is the health of your fish and your subsequent enjoyment of our hobby.