How To Set Up A Fish Tank and Common Mistakes Beginners Make

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Fishkeeping is an extremely popular and rewarding hobby. In fact, a recent survey shows that some 11.5 million freshwater fish are U.S. household pets.

But there’s a lot to learn if your fish are going to thrive. 

For example, is a tropical freshwater aquarium the best choice for a beginner? What about introducing new fish to old fish? And how many fish per gallon of water can you keep? 

Read these guidelines on aquarium basics to learn how to set up a fish tank without making the most common newbie mistakes.

How To Set Up A Fish Tank

There’s a lot more to setting up a fish tank than simply filling the tank with water and putting some fish in it! 

hands of aquarist preparing substrate in aquarium for planting water plants

Here’s how to do the job properly!

Preparing for a Successful Aquarium and Healthy Fish

The key to successful fishkeeping is to learn as much as you can about all aspects of the hobby. So, before you rush out and buy everything, do some research and learn as much as you can.

In short, good preparation is crucial for a trouble-free tank and healthy, thriving fish.

Learn About the Water You Will Be Using

It’s widely accepted that a freshwater aquarium is the best choice for a beginner rather than a saltwater setup. 

So, in this guide, we discuss setting up a freshwater fish tank.

Water is just water, right? Yes, that’s true, but there are several different kinds of water that you can use to fill your aquarium:

Tap Water

Most people, including myself, use tap water for their fish tank.

Municipal tap water for use in your home is treated to kill most bacteria and parasites so that the water is safe for you to drink and wash in. Consequently, tap water contains chlorine or chloramine that’s used as a decontaminant, as well as some heavy metals.

Before adding tap water to your aquarium, you must add a dechlorinator or water conditioner product to remove harmful substances, specifically chlorine and chloramine, both of which are highly toxic to fish.

Well Water

Well water doesn’t contain chlorine, but it can still contain contaminants such as nitrates and coliform bacteria from agricultural runoff and various chemicals found in paint, solvents, pesticides, and herbicides.

The pH and hardness of well water varies, too, and it’s often oxygen-depleted.

Bottled Water

Bottled water is usually spring water, filtered water, or well water, and it can contain added minerals that are harmful to fish. There may also be chlorine present, so you still need to treat the water before you can safely use it in your fish tank.

Also, bottled water is very expensive. 


Rainwater seems like a cheap, healthy option to use in a fish tank, especially if you have the space for a water butt in your backyard. 

However, rainwater has a low mineral content, and the pH tends to vary, so you need to treat and test it before using it for your fish.

Pro Tip 

If you live in an urban area, rainwater can contain atmospheric contaminants and pollutants such as smoke, chemicals, and exhaust fumes. And rainwater in a butt or barrel can harbor bacteria and parasites that could harm your fish.

Distilled Water 

Distilled water is free from most contaminants, but it also contains virtually no minerals. So, you would need to remineralize the water before using it in your fish tank.

Also, the volume of water you would need for a large tank makes using distilled water impractical and expensive.

Reverse Osmosis (RO) Water

Reverse Osmosis water is specially produced for use in aquariums. R.O. is a process where water is filtered to remove contaminants, including chlorine, minerals, and some forms of bacteria. R.O. water is a popular choice for aquariums, although you do need to remineralize it.

You can buy R.O. water in fish stores or purchase an R.O. filter for use in your home. 

Deionized (D.I.) Water

Pouring treatment to water

Deionized Water is produced by using resins to capture electrically-charged pollutants and switch them for harmless charged particles. 

Although free from mineral and chemical contaminants, D.I. water can still contain bacteria, and you will need to add minerals to make the water suitable for use in an aquarium.

Learn All You Can About the Fish Before Setting Up Your Aquarium

Before you can set up your tank, you need to know what species of fish you’re going to keep.

Most beginners like to keep a community tank that contains a variety of different fish species. Research the fish species you would like to keep and check their compatibility, taking into account:

  • Size
  • Temperament
  • Preferred water temperature
  • Preferred pH range and water hardness
  • Diet
  • Behavior
happy mother showing to her child a fish bowl with gold fish inside

Ideally, you want to pick peaceful fish of a similar size, share the same requirements in terms of water parameters, swim in different water column areas, and eat a similar diet.

Once you understand more about the behavior of the fish you want to keep and their natural habitat, you can buy the right decorations, plants, etc., for your tank.

Setting Up the Aquarium

You will need the following for your aquarium, all of which you can buy from your local fish or pet store.

  • Fish tank
  • Aquarium stand or cabinet
  • Sand or gravel substrate
  • LED lighting unit (if not included with the tank)
  • Filtration system (if not included with the tank)
  • Water conditioner
  • Heater (if you want to keep tropical fish)
  • Aquarium thermometer
  • Tank decorations, such as driftwood, rocks, resin ornaments, etc.
  • A selection of live plants
  • A fish net
Beautiful planted tropical freshwater aquarium with fishes. Aquascape.

Now, you can set up your aquarium!

Choose Where To Put Your Fish Tank

You need to pick a suitable location for your fish tank:

  • Avoid putting the tank where it will be in direct sunlight, which encourages algae growth and might overheat the water.
  • Don’t put the tank next to a heat source or in a draft.
  • The floor must be level so that there’s no risk of the tank tipping over.
  • Don’t put the tank in a doorway or place where it could be knocked by running kids or pets.
  • You need a mains socket close by so that you can plug in your filter, lights, and heater.

Also, you’ll need to perform partial water changes every week, so the tank should ideally be within reach of a faucet and sink.

1. Clean The Tank

Use a clean cloth or kitchen towel to wipe down the inside of the tank with clean, warm water. Do not use soap or detergent.

2. Wash The Substrate

Put the substrate in a colander over a plastic bucket and wash it under cold, running tap water. Give the substrate a good stir, drain, and repeat until the water is clear.

If you’re using an undergravel filter, install it now.

3. Add The Substrate To The Tank

Add a couple of inches of the substrate to the bottom of the tank.

4. Wash And Add Your decorations

Now, have fun aquascaping your new tank

Wash your decorations under running water to remove dust, and then arrange them in the tank as you wish, but save your living plants until later.

5. Add The Heater And Filter

Fit the filter and heater in the tank but don’t switch them on yet.

If using an air pump, don’t put it inside the tank.

6. Fill The Tank With Water

Before you add tap water to your tank, you must treat it with a water conditioner to remove chlorine and chloramine, both of which are very harmful to your fish.

To avoid displacing the substrate, pour the water over a rock or put a small plate onto the substrate and slowly pour the water over that.

7. Add Your Plants

Add your live plants, putting the tallest at the back and sides of the tank and the smaller ones toward the front and midground. Allow space between the stems for growth and spread.

Live plants require eight to ten hours of light per day for photosynthesis, so you’ll need to set the lighting unit’s timer.

8. “Seed” The Water

Before you can add fish to your tank, you need to cycle the aquarium. To kick off the nitrogen cycle, add a pinch of fish food or a few drops of pure ammonia to seed the water.

9. Switch On The Heater And Filter

Switch on the heater and filter system.

10. Allow The Tank To Cycle

Before adding your fish, you need to wait until the tank is fully cycled. Check the water daily with an aquarium water testing kit. When the levels of ammonia and nitrite are zero and nitrates are around 20ppm or below, it’s safe to add a few small fish.

Allow a week or two before adding more fish so that you don’t overload the biological filter.

Common Mistakes Beginners Make

In no particular order, here is a list of the most common dummies’ mistakes that beginners make so that you can avoid these schoolboy errors!

1. Adding Fish Before The Aquarium Is Ready

When you have your aquarium set up and beautifully aquascaped, it can be very tempting to rush out and fill it with fish. 

But wait!

Beginners to the hobby often don’t realize just how important it is for the tank to be fully cycled and for the water parameters to be stable before the fish are added. If you introduce your fish to the tank before it’s properly cycled and the water parameters are correct, you risk killing your new pets.

So, use an aquarium water testing kit to make sure that:

Male hand holding PH tests in front of freshwater aquarium.
  • the levels of ammonia and nitrite are zero
  • nitrate levels are below or close to 20ppm
  • the water pH and hardness are within the fishes’ tolerance levels
  • use an aquarium thermometer to make sure that the water temperature is correct for the fish species you’ve chosen

Once all those things are in place, you can add fish to your tank.

2. Adding Fish Without Acclimating Them First

Most fish species can be susceptible to temperature shock. By the time you’ve driven home from the fish store with your new fish, the temperature in their plastic bag of water will most likely not be the same as that in your tank.

Untie the knot in the top of the bag so that air can get inside. Now, float the bag on top of the tank water for 15 minutes or so to allow the water temperatures to gradually equalize. Then you can release the fish into the tank.

3. Buying A “Small” Aquarium 

Beginners often buy a very small tank, thinking that it will be easier to maintain than a big one. That’s true in that a large tank is more expensive, will be more complex to set up, and takes longer to clean.

However, a small tank presents its own problems. In a small tank, waste products can build up very quickly, so you’ll need to carry out more frequent water changes and filter maintenance. If you don’t do that, the water quality can quickly become unsanitary, which will make your fish sick, and you might even lose some.

I recommend that you start with a 30-gallon to 60-gallon aquarium, depending on how much space you have in your home.

4. Buying The Aquarium and Fish Together

As we explained above, you can’t set up your aquarium and add fish to it straight away. You need to cycle the tank first and then add a few fish every week or two, so as not to overload the biological filter.

If you see a fish you particularly want, such as a beautiful betta, most fish stores will allow you to place a deposit on the fish so that you can come back and collect it once your tank is fully cycled and ready.

5. Impulse Purchases

Most of us have done it! You see an unusual fish, and you buy it on impulse.

Resist the urge to impulse-buy. Go home, research the fish thoroughly to see if it will fit in your community, and go back another day if you still want the fish.

6. Underestimating The Running Costs

Hand Holding Tag Colored Vector Illustration

Beginners frequently underestimate how much it will cost to run the tank. You’ll need to factor in:

  • Electricity required to run the filtration system, heater, and lights
  • Fish food
  • Aquarium water testing kits
  • Fish medication
  • Water conditioner
  • Replacement filter media
  • Replacement light bulbs

7. Not Understanding The Nitrogen Cycle

To keep a healthy, thriving community of fish, you must understand how the nitrogen cycle works and why it’s so important.

The nitrogen cycle is pretty easy to understand and manage, but getting that wrong or ignoring it altogether will certainly result in your fish dying.

To read an in-depth beginner’s guide to the nitrogen cycle, click this link.

8. Accidental Poisoning

Unfortunately, it’s extremely common for newbies to accidentally poison their fish.

Poisoning generally happens due to poor tank maintenance, specifically:

  • Failure to carry out weekly water changes
  • Forgetting to clean and replace filter media
  • Not vacuuming the substrate to remove decomposing fish waste, plant debris, etc.
  • Using too many chemical treatments

9. Not Using Live Plants

Live plants are extremely beneficial for your tank for the following reasons:

  • Oxygenate the water
  • Absorb nitrates from the water
  • Provide shelter for timid fish and fry
  • Add aesthetic value
  • Starve algae of nutrients

There are plenty of beginner-friendly plants to choose from, too!

10. Using A Cheap Filter

Many beginners buy an aquarium starter pack that includes a filter. Unfortunately, many of those filters are not powerful enough to keep the water clean.

Ideally, the filter should circulate the water around the aquarium and through the filter media at least four times per hour. 

11. Not Testing The Tank Water Regularly

Litmus strips for measurement of acidity.Beaker with water

With a brand-new tank, it’s essential that you test the water every day. Once the tank has settled and stabilized, you need to check the water monthly.

You need to check:

  • Ammonia
  • Nitrites
  • Nitrates
  • pH level
  • Water hardness

Most fish health problems and disease outbreaks stem from poor water quality, so routinely checking the water is crucial.

12. Insufficient Water Changes

As mentioned above, if the water in the tank is dirty and full of toxic substances such as ammonia, nitrites, and nitrates, your fish will die. Period.

Cleaning the aquarium. Pumping water out of the aquarium. Close-up. Siphon Gravel Cleaner Tool In The Aquarium. Aquarium fish content and hygiene concept.

You need to carry out partial water changes of between 25% and 40% every week, depending on the number and species of fish you keep. 

13. Washing The Filter Media In Tap Water

Washing your filter media in tap water is a classic newbie error that can spell disaster for your fish.

Tap water contains chlorine or chloramine, both of which are lethal for the beneficial bacteria that live in your biological filter media. Without those bacteria to process the ammonia in fish waste and decomposing organic matter, the water in your tank will be toxic to your fish.

Always wash filter media in the dirty tank water that you’ve removed during a water change.

14. Changing All The Filter Media At Once

If you remove all the filter media, you’re also removing the colonies of beneficial bacteria that live there. When replacing spent filter cartridges, allow a week or so between replacing each piece of media.

15. Overstocking 

Overstocking your tank overloads the biological filter, leading to toxic water.

Also, fish need space to swim and grow. If the tank is overcrowded, the fish will become stressed, and fights might break out, depending on the species.

16. Overfeeding

Although your fish might appear hungry, overfeeding can cause health problems such as bloat and constipation. Also, uneaten food simply decomposes in the tank, polluting your water.

17. Keeping Incompatible Fish

Some fish are very aggressive, whereas other species are totally peaceful, and some can be peaceful, depending on what fish they are kept with.

To avoid carnage in your tank, be sure to do your research and only choose fish species that are compatible.

18. Rearranging The Tank

detail of man's hand coming out of the aquarium during his cleaning. Household chores concept

Although you might want to change things up in your tank from time-to-time, that can totally confuse and stress your fish.

Decide on the look you want for your aquarium and stick to it.

19. Failing To Treat Algae Properly

Algae often grow in freshwater fish tanks, covering the glass, decorations, and even plants.

The algae growth can be prevented by following these tips:

  • Keeping the tank out of direct sunlight
  • Including live plants in your setup
  • Cleaning the glass and decorations to prevent algae from building up

Although it’s not necessarily harmful, algae don’t look nice and can clog your filter if allowed to cover the inlet and outlet.

20. No Maintenance Schedule

Vilnius, Lithuania A man vacuums a fish tank.

A regular maintenance schedule for your tank is essential if you’re going to avoid problems with water quality and fish health. You’ll need to include:

  • Water changes
  • Filter cleaning and maintenance
  • Tank cleaning
  • Water tests

You will need to allow at least an hour or more per week, depending on the size and complexity of your setup for maintenance.

21. Over-cleaning or Under-cleaning

Many newbies are either too diligent when it comes to cleaning the tank or not diligent enough!

Over-cleaning your tank can be damaging, as that can result in you removing all the beneficial bacteria that you need for efficient biological filtration. Conversely, if you don’t clean the tank often enough, the water quality will suffer.

22. Failing To Quarantine New Fish

Although it’s tempting to add new fish to the community straight away, you must put them in a quarantine tank for at least ten days first.

During that time, you can observe the fish to make sure they’re healthy and free from disease and parasites before introducing the newbies to your existing stock.

23. Wrong Aquarium Positioning

As mentioned earlier, the correct, safe position of your fish tank is crucial for fish health. 

Read the article at this link for guidance on where to position your fish tank.

24. Not Using Suitable Lighting

Some fish don’t appreciate bright lighting. Also, most plant species need a certain amount of light to thrive and grow.

Research fish and plants before you buy them to make sure that their lighting requirements are the same and fit the lighting unit you have in your tank.

25. Too Many or Too Few Decorations

Fish tank with rocks, plants and fishes

The fish should be the stars of the show in your tank, not your ornaments! 

Although many fish species appreciate somewhere to take shelter and others like to explore caves, rockwork, and driftwood, don’t’ cram too much into the tank, or you’ll fill all the swimming space that the fish need.

On the other hand, too few decorations can leave a tank looking sparse and bare, and the fish can feel insecure and too exposed. 

26. Not Using An Aquarium Lid

If you don’t want a large hood on your tank, you should use a cover slide instead because:

  • Some fish can and do jump
  • Dust and contaminants might fall into the water
  • An open tank encourages water evaporation

27. Adding Fish That Might Outgrow The Tank

Swimming Giant Iridescent Shark

Most fish sold in fish stores are juveniles with growing still to do.

Research the fish you’re thinking of buying to make sure that it won’t grow too big for your tank when it’s fully grown unless you’re prepared to upsize your aquarium in the future.

28. Direct Sunlight

Many beginners put their tank where it will get direct sunlight during the day, often mistakenly thinking that the fish will enjoy the sun, their plants will grow better, or that they won’t need a light in their tank.

Unfortunately, direct sunlight is very damaging for your tank:

  • Algae will grow more vigorously in sunlight.
  • The water temperature will heat up very quickly, potentially stressing or even killing your fish.
  • Bright light will stress your fish.

29. Leaving Your Fish To Your Neighbours While On Vacation

When you go on vacation, don’t leave your fish in the care of your inexperienced, non-fishy neighbors. That’s sure to end in tears!


  • Clean your tank and rinse your filter media right before you go on vacation.
  • Use an automatic fish feeder to deliver food for your fish at pre-set times every other day.
  • Set a timer on your lights so that plants receive sufficient light.

30. Not Having A Back-up Plan For Power Failure

A prolonged power failure can wreak havoc in a fish tank. The filter and heater will fail, water quality will suffer, and the fish could suffer temperature shock.

Make sure you have a back-up plan in place for power outages. That might include using a battery to power your filter system or using blankets to wrap around the tank to preserve heat.

In Conclusion

I hope you enjoyed our guide on how to set up a fish tank.

Before embarking on your fishkeeping adventure, do your research, learn all you can about the hobby, and use all the resources here for you at to make sure you avoid the common mistakes made by newbies!

Don’t forget to share this article if you found it helpful.

Alison Page has been an avid fish keeper for over 35 years and has owned many different species of freshwater tropical fish including bettas. Currently Alison has two large freshwater tanks. The first tank has two huge fancy goldfish who are almost ten years old and still looking as good as ever. In the other, she has a happy community of tiger barbs, green tiger barbs, corydoras catfish, platys, and mollies.

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