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Setting up an Oscar Fish Tank

If you've decided that you are serious about keeping Oscars then it's time to start looking at exactly what requirements one of these fish need. First and foremost Oscars can easily exceed 12 inches in size and weigh up to 3 pound in weight. Any sensible person should realise that a fish like this cannot be housed in a small aquarium, it is just not fair and it will never work in the long run. Some people try and keep Oscars in small aquariums but they nearly always run into problems with water quality which in turn will lead to serious health problems with the fish. It's important to be honest with yourself, there is a world of difference between keeping a small goldfish in a bowl compared to keeping a large Oscar fish.

So what size tank should you be considering if you are thinking about getting an Oscar? Thankfully experienced Oscar fish keepers around the world have now come to agree that one single adult Oscar must have AN ABSOLUTE MINIMUM of 55 gallons of water to itself. There isn't any argument about this figure, keeping them Oscar in less than 55 gallons will only lead to water quality problems. Even with 55 gallons you are going to have your work cut out keeping the water at a quality that will keep the fish healthy. So if you are planning on keeping two Oscars then it's quite simple, you will be looking at an aquarium in excess of 100 gallons. Obviously once you start going down the realms of wanting Oscars, plus tank mates you're looking at a pretty substantial aquarium well in excess of .   

I cannot emphasise how important it is that you keep your Oscar in the correct size aquarium. A large Oscar housed in an aquarium that is too small will result in water quality that will deteriorate very quickly indeed. It will be virtually impossible for you to maintain water quality that is anywhere near acceptable for an Oscar fish to live in.

You may be wise to look upon keeping Oscars in the same way you would if you are committing yourself to a pet dog. Oscar Fish can live up to 15 years +, longer than most dogs. It makes perfect sense to give your fish the best home you can from the very beginning. 55 gallons is the absolute minimum for somebody who cannot go any bigger, if you can accommodate a much larger tank than my advice would be to go for it, I promise you that it would be the best thing for your Oscar in the long run.

Use a Secure Aquarium Lid

Oscar fish are well known for jumping in the aquarium. We have had numerous documented cases on the forum where the Oscar has physically jumped completely out of the aquarium and in some cases has perished because its owner was not aware of the situation. Sometimes Oscars will jump at night, maybe they have seen small flies above the tank. The owner has then come down in the morning only to find the dried up corpse next to the tank. So it's very important that you have a secure lid on your aquarium at all times that will stop your Oscar from jumping out.


Calculate how much water you aquarium holds

It is absolutely vital that you know exactly how much water your aquarium holds. If you have purchased it new then you should already know. However if you have purchased a used aquarium then it's not always easy to calculate just how much water the tank will hold. We have a simple calculator that will tell you approximately how much water you aquarium will hold. Simply measure lamps depth and height, enter the information into our calculator and you will get the answer in either the UK or US gallons. It's extremely important that you measure exactly how high the water comes up the tank, don't simply measure the height of your aquarium because water doesn't always reach the top.

Go to our aquarium size calculator now

More Than Two Oscars Living Together

Some advice given on websites and forums suggests that more than two Oscars will not be able to thrive together in harmony. This is actually not true, three, four, five or even more can live together perfectly okay as long as they have plenty of room to do so. If Oscars are forced to live together in a cramped space then you run the risk of serious aggression. Keeping more than two Oscars together would of course require a sizeable aquarium, at least 180 gallons. One thing to bear in mind if you are keeping more than two Oscars is what happens if two of the Oscars decide to form a pair and start breeding? Common consensus suggests that it's probably best to keep no more than two Oscars together, I would probably agree with this in principle.


Why Filtration Is Very Important

Having the proper sized tank is really only part of the equation. In order for fish to survive and live longer than a few days, you need some way of removing all the dangerous toxins from the water that are so dangerous to fish. This is what your filtration is designed to do, keep the water completely clean of toxins and therefore make sure that the fish always has a clean environment to live in. Understanding just how important your filter is is really very important and is often completely overlooked by people who want to keep fish. The following information will tell you everything you need to know about your filtration and what it does. In order for you to understand how your filter works, it's a good idea to also know what happens when fish produce waste and what happens to that waste, this is called the nitrogen cycle. Read the following on how to cycle a fish tank, it will also explain how the nitrogen cycle works


What Is Filter Media and How Does It Work?

Before we start talking about filters and which ones are best suited to an Oscar fish aquarium, I thought it would be a good idea to introduce you to what is inside your filtration system. The innards of a filter is rather like your kidneys and liver, they basically perform the same function, to remove all the waste and horrible stuff. 

There are two types of media that you will become very familiar with, each one is quite different and must be treated accordingly.


Japanese filter matting

Mechanical Filtration

performs a very important task within your filtration system. I'm sure you know what you use a food strainer for? Well mechanical filtration is really no different. When the filter takes water from your aquarium, it first passes through the mechanical media which helps remove any solid waste, and some food, vegetation, fish waste etc. However, the mechanical filtration is coarse enough so it allows water to flow freely through it. You can get what we call polishing pad is, these are slightly finer and are designed to catch very small particles of waste. These can be placed after the main mechanical filtration. But you must be aware that very fine filter media may become saturated with waste fairly quickly. When this happens, the water flow will be restricted and you will not get the flow rate that you need. Personally, I never use these very fine mechanical filtration pads, is just not worth the hassle, with Oscars, they are so dirty that you are for ever changing them.

The most effective mechanical filtration media I have found over the years is Japanese matting. You can buy it in fairly sizeable quantities for a very reasonable price off of eBay. I think the last one I bought was almost the size of a single mattress, so you can imagine it lasted me for absolutely ages, I just cut it to size when needed. If your filter is fairly sizeable then there is no reason for you not to use more than one piece of Japanese matting. However, Mace canister filters are probably best limited to one piece. I was able to fill one whole compartment in my some filter with Japanese matting, that gave me superb mechanical filtration and nothing got through. You will always need to clean mechanical filtration, there's no way to get around this task. Even though mechanical filtration isn't quite as critical as biological filtration, as in protecting your bacteria, but we would still advise you to use existing tank water to clean it. Mechanical filtration will always contain some nitrifying bacteria that can only be beneficial to you.


Biological Filtration

bacballs biological filtration is very different from mechanical filtration. Sometimes it can look the same as some filters use sponge for their biological media.

But it's very important that you understand that they perform completely different tasks from one another. It's called biological media because that is where the living bacteria congregate and grow. Mechanical filtration catches solid debris, bio media consumes ammonia and nitrite, the dangerous toxins that can result in fish death. Biological filtration must be treated very carefully as you don't want to upset the bacteria colony that live on the media. So whereas it will need to be washed occasionally, be very careful when you do clean it, use an existing bucket of tank water, but don't overdo it don't think you have to get it sparkling clean, just remove any solid bits of debris that may have slipped through the mechanical filtration. One very very important thing you must always remember is that the bacteria that live on your bio media need oxygen to survive. They get the oxygen from the water flow through the filtration system. It's a common mistake by newcomers to switch off their filters, sometimes overnight, or because they may be a little bit noisy. This is probably the worst thing you can ever do because the bacteria will start dying if they are deprived of oxygen. So if you need to switch your filtration off during cleaning, limit the time it's off, never let the biological filtration dry out either, follow these two rules and you will be okay.


Chemical Filtration (activated carbon)

activated-carbon aquarium filtration can be recognised as it is normally black in colour. Also known as activated carbon it is often contained in new filters. The consensus between a lot of us fish keepers is that activated carbon is really not needed and shouldn't be left in your filter. The actual purpose of chemical filtration is to remove impurities from the water. Some people use chemical filtration after they have medicated attack, it can act as to remove any leftover medication. There is a suggestion that once activated carbon becomes saturated with impurities, they can somehow leach back into the aquarium water. I've also read articles that directly relate activated carbon to hole in the head disease. This is something that I can't substantiate for sure, but I thought it was probably worth mentioning.


Aquarium Filters for the Oscar Fish

We have already determined that Oscars need large aquariums. A large aquarium will need plenty of filtration in order for it to remove the toxins from the water efficiently. We know that Oscar fish are extremely messy, not only in their eating habits but also in the amount of ammonia that they produce. Don't assume that basic aquarium filtration is going to be enough, I can tell you that it won't be. So for instance if you have purchased one of these complete setups that already has an internal filter built in, you are going to have to do increase the filtration considerably.

There are thousands of different filters on the market, you need to choose one that matches not only the aquarium you've got, but also the species of fish you are going to keep. If you're buying a filter from you then look at the specifications, they will tell you exactly what size tank the filter is made for. The specifications will normally also tell you the maximum size tank canister will filter. However, don't be fooled into thinking that if the specifications state that a certain filter can filter up to 600 L you are good to go with one filter. Remember that we are filtering a tank with large messy fish, you need to double the filtration in order to make sure the water is completely free of toxins and waste. So a canister filter rated for a tank up to 600 L would be perfect for a 55 gallon tank. However you would need a couple of these are 125 gallon tank. The range of are perfect for the smaller tanks. However, you would need to use two on a 125 gallon tank for instance. Once you start getting into the larger tank range then I would advise you to look at the range of canister filters as they make models that can filter up to 350 gallons.

 Compared to other types of aquarium filter such as internal or hob filters, Canister filters offer far greater efficiency as they can accommodate far more filter media than most other filters. They are also very flexible as you can vary the amount of different media used, in other words if you want to use more mechanical filtration then this is possible with canister filters. There are also referred to as external canister filters because they are housed outside of the agrarian, normally underneath in the cabinet. They utilise two pipes, an intake and a return pipe. The intake carries water from the aquarium which then enters the filter, flows through the media and then is taken back to the aquarium via the return pipe. The advantage with canister filters is the intake pipes are designed to pull not only water, but also solid waste from inside the aquarium. Most canister filters are equipped with "spray bars" which are connected to the end of the return pipes, they are designed to distribute the water over a larger surface area thus oxygenating the water efficiently.


One of the biggest advantages with these type of filters is that they can often be left for two or three weeks in between cleaning which obviously makes tank maintenance easier. Obviously the more filtration you have on your aquarium, the more efficient it will be and the longer it can be left in between cleaning.


The Aquarium Sump Filter

Some fish keepers who have installed very large aquariums that are often heavily stocked install a on their aquarium. These type of filters are very much for people who are experienced with keeping fish. We wouldn't normally recommend installing a sump filter unless there is an absolute need for it. Further Reading on Sump Filters...


Don't Turn Your Filters off for Too Long

The bacteria that live in your filtration system must be looked after carefully. In order for the bacteria to survive and perform properly they need oxygen and a surface to live on. Therefore it is recommended that you keep your filters running at all times and only turn them off when you need to. There is a lot of debate as to how long bacteria can survive without oxygen and new research recently has blown a lot of common consensus out of the window. It is now thought but not absolutely proven that your biological bacteria can  survive for much much longer than we ever thought. It's also thought that these nitrifying bacteria can survive inside bottles by switching their metabolisms which results in resting cells. This could explain how bacteria in the bottle really does work.  Having said all this I would still strongly advise you to keep your filtration system running at all times as this will keep your bacteria nice and healthy.

Aquarium filtration can be expensive, however you will probably pick up a good bargain on eBay 


Heating Your Aquarium

Oscar fish come from the tropics so in most cases your aquarium will need some kind of heating device to keep the water at the correct temperature. Oscars are quite happy living in water temperature between 21°C and 29°C. An optimum temperature would probably be around 27°C.

When it comes to installing heating in your aquarium I would advise you to choose the heaters very carefully. Oscar fish can be very destructive and believe you me they have the capability to smash glass heaters to bits. If you don't mind spending a bit of money on heaters then the best heaters I have ever come across are made by Aqua Medic. These heaters are manufactured from titanium and are virtually indestructible, they will even withstand being taken out of the water, unlike many other heaters which will break if they are not submerged under the water all the time. Obviously not everybody wants to spend the best part of 100 quid on heating, so thankfully there are quite a few good quality heaters on the market that I would certainly recommend as being suitable for an Oscar aquarium. 

Aquarium heaters are best placed next to the return pipe, or spray bar so that the water can be heated uniformly as it enters the tank. Always remember to switch your heaters off before you start taking water out of the tank, i.e. when you change your water. This is one of the mistakes people make and then they wonder why the heaters don't work after. You can get in line heaters that don't need to be placed inside the aquarium. If you have an Oscar that is particularly destructive then you may want to look at one of these in-line heating systems. I've used something similar myself so I know that they do work extremely well. I've chosen a video from YouTube which should give you an idea of how these heaters work and what people think of them.


Aquarium Thermometers

Aquarium thermometers were always the bane of my life, I never found an internal thermometer that the Oscars wouldn't find and destroy. The best advice I can give you is to completely forget about putting thermometers inside the tank, you'll be wasting your time if you've got Oscars. The best thermometers I have used are external and therefore out of the reach of destructive Oscars. You don't have to pay a fortune, you can get one for £10 and it will last you for years.


Maintaining Oxygen Levels

Something that is often overlooked is maintaining oxygen levels in your aquarium. People are often under the assumption that fish don't need oxygen because they live in water. It's quite the opposite actually, fish need oxygen to survive. If your water is deprived of oxygen than your fish will die. It's extremely important that your water is kept oxygenated at all times, especially in the warmer months of the year when aquarium water can increase in temperature and oxygen levels drop. Fish use their gills to obtain dissolved oxygen in the water, so there are a few important things you need to remember. The filtration system should be adjusted so that the water leaving your return pipe creates surface agitation which in turn will oxygenate the water. Most canister filters come with spray bars which are designed to spray water over a larger surface area, thus creating oxygen in the water. It's also important to remember that the smaller the area of water, the less oxygen that will get dissolved into your aquarium water. So if your tank is not particularly big, it's even more important that you make sure that oxygen levels are kept up. If you have plants in your aquarium then remember that they will consume more oxygen during the night time period so you may want to run some kind of air stone at night time.


Aquarium Lighting

Oscars do not require any specialised lighting, in fact you could probably leave the lights off all day and it wouldn't bother them in the slightest.

However, we have all gone to the trouble of setting up an aquarium so it's obviously nice to be able to see what's going on. It's even nicer if you can use lighting that brings out the colours in your fish, although many Oscars are rather dull and drab. Having said that, lots of tropical fish do have beautiful colours that can be wasted if the aquarium lighting isn't very good. use the Kelvin rating, this is basically the colour temperature of the light, the full spectrum of light produced by the sun which consists of different wavelengths. I know, pretty boring and not really that interesting to talk about unless you are an aquarium lights enthusiast. 

 The best advice I can give you is to think about what type of lighting you want to achieve. Most people want to see their fish properly, may be the colours popping. Therefore depending on how many bulbs your system takes, you could opt for one Marine blue and one Marine white. Maybe you've got a large aquarium which takes three bulbs, you could opt for two Marine blue and one Marine white, or vice versa. It's impossible for me to tell you exactly what you need, the best thing to do is go to the fish store and see what's available, I'm sure they could give you some really good advice. Alternatively come and talk to us on the forum and somebody will be happy to advise you on lighting.


 Don't Leave Your Lights on Too Long

A lot of people wonder why they have excessive algae growth in the aquarium. There are several factors that can encourage algae growth, however the most common reason for algae is excessive and prolonged in the aquarium. The tropics receive approximately 12 hours of light a day. However if you try and replicate that in your aquarium value are going to encourage algae growth. It is recommended that limit the time you have your lights on to around eight hours a day. Having said that, I only put my lights on in the evening when it starts getting dark, this seems very little point in having your aquarium lights blazing away in the middle of the day, especially if you are not really in the room.


Substrate Rock and Wood

I've always preferred to have substrate in an aquarium, without a bed the aquarium just looks completely barren, I can never understand people who have a bare glass bottomed tank. My advice would be to opt for either gravel or sand, these are the most common types of substrate people use, they are readily available, cheap and very easy to maintain.

Sand is my favourite substrate, it's easier to maintain than gravel as debris does not get embedded underneath where it can be missed when cleaning. You can use basic play sand which is readily available from builders merchants. Alternatively aquatic suppliers so all different types of sand, they come in different colours and grades. Always clean sand before putting it in the aquarium if you have bought it from a builders merchant. It's very easy to clean, use a bucket and just swill portions of sand with water. If you have bought dedicated sand from an aquatic store then it's probably already been prewashed so you can put it straight in your aquarium. Don't be tempted to put too much sand in your aquarium, probably no more than 1.5 inches of substrate, any more and you are just using up space that could be used for water. Sand is extremely easy to clean, you simply hover your gravel vac about an inch above the sand and use the power of the syphon to lift any debris which will collect on top of the sand.

Gravel also comes in various sizes and colours. If you buy from the aquatic store then you'll be paying quite a lot of money. My advice would be to buy a large sacks of gravel from the builders merchant. It will need thoroughly cleaning to get rid of all the dust. Again, don't put too much in the aquarium, about 1.5 inches. Gravel needs cleaning more thoroughly than sand once in the aquarium as dirt and debris can get submerged. You will need to use a gravel vac to clean it properly, you have to push the gravel vac into the gravel and wait for the water to run clear.

I love a mixture of wood and rock in a large aquarium, it's very easy to replicate what it might look in the wild. Unfortunately prepared aquarium wood is extremely expensive for the larger pieces. Smaller pieces of wood can be bought for around £5, but these would be lost in a very large aquarium. Expect to pay in excess of £50 for a large piece of wood. There are various different types of wood available, these can be found at reputable fish stores. You will be advised not to put any all pieces of wood to find in your aquarium. You just don't know where it's been, it could be coated in preservatives which could be toxic to your fish. 

Rock can look absolutely beautiful if placed properly in an aquarium. However you've got to be a little bit careful which will rock you do use as some of it can have an effect on the chemical balance of the water. For a better understanding of what type of rock is suitable for aquariums please check this article out

If you want ornaments in your tank, make sure they are clean and free from paint that may contain lead or impurities. You can normally find plenty of purpose made items at the aquarium store . If you are unsure in any way, you are probably better off buying from somewhere that supplies aquatic equipment. I often get pots from garden centres. One of my catfish has made a large pot his home. I have even seen one of my Oscars sleeping in the pot at night.


Plants and Oscar Fish

Putting plants in the same aquarium as an Oscar Fish is rather like leaving a box of doughnuts in front of a really fat bloke, neither will last very long. Joking aside, people have tried to keep live plants with Oscars but most have failed. Don't ask me why, but Oscars seem to take great pleasure in completely destroying any plants that are growing in their aquarium. There are exceptions as some people will tell you, but the consensus is that you shouldn't even bother planting your tank out if you are going to be keeping Oscars.

However, plants do look nice, they make the aquarium look very attractive. Rather than wasting your money and time with live plants, why not try putting in some fake plants. There are some really authentic looking fake plants on the market that looks extremely realistic. Don't be under the misapprehension that Oscars will leave fake plants alone, the chances are they will probably use them as their own personal entertainment. However fake plants will definitely last a lot longer than life plants and you can just replant them if they get uprooted.


Give your Fish Shelter

Most fish love hanging around structures, they use it for shelter when sleeping, or somewhere to stalk pray when hunting. Fish will often hang around rocks if the water is flowing fairly fast, they can often catch food as it flows by. So it makes sense to try and replicate this in your aquarium, give your fish somewhere to retreat to if they feel threatened. Some fish must have somewhere to hide, without somewhere for them to to go and feel safe they may get very stressed. 

There are lots of different things you can use to make up structures and hiding places for your fish. For instance, a large ceramic plant pot is often the perfect hiding place for fish like catfish, or clown loach, they will often make places like this their permanent home. If you can get hold of some large pieces of rock then you can construct a cave which is perfect for fish to hide in. If you place a rock so that there is a nice gap at the back then this is often where fish like to go when they want to feel safe. How about a large piece of wood? Not only do large pieces of wood look awesome, they are also very authentic, especially if you are replicating the waters in the rainforest. Whereas my Oscars never really used rock to shelter, they used to love resting up behind a large piece of wood. In fact, they would often get very very annoyed if the word was ever moved during tank maintenance.


Changes in Oscars Aquarium

The Oscar could quite rightly be described as being quite an intelligent fish. However an Oscars brain is still very primitive so their intelligence shouldn't be compared to that of a dog, or even an octopus. Oscars are very inquisitive fish and will notice changes in their environment. For instance, they can sometimes show what people would class as an annoyance when things are moved around in their tank. I have observed my Oscars investigating a large crater that was formed by water coming from the hosepipe during a water change. It wasn't there before and they were obviously well aware of this. If your Oscars do show signs of stress or anger when things change, just give them time, they should settle down except and get used to changes.


Oscar Fighting - Rearrange their Tank

So you may well ask how do you stop your Oscars from fighting? If you've got Oscars that hate each other, the chances are they will keep on fighting whatever you do. However, sometimes the simple procedure of rearranging their aquarium can stop Oscars from fighting. This can often help when introducing an Oscar into a tank that already has an Oscar in it. Oscars are very attentive fish that are well aware of their environment. If you rearrange everything in your Oscars tank, this will often take their mind off the fighting. Unfortunately I can't guarantee a long-lasting truce.

Electricity Usage

Don't be under the misapprehension that owning a large aquarium is going to be cheap. Before you think about installing that huge aquarium, ask yourself whether you are going to be able to afford to run it 24/7. Remember that a large tropical aquarium will need plenty of filtration and heaters running every day all year. I never actually calculated exactly how much my 300 gallon aquarium cost to run, actually I haven't got it any more, I sold it a few months ago. My monthly direct debit electricity bill has recently been amended by a reduction of over £60. Nothing else has changed, electricity hasn't increased recently, the only thing that has changed is me not having the large aquarium to light, filtrate and heat all year round. So you can work the sums out for yourself, it looks as though I were spending several hundred ££'s a year to run my aquarium.

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