Beginner’s Guide to Set Up a Freshwater Aquarium

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For many, fishkeeping looks like an easy enough hobby, but hear me out when I tell you that there’s more to it than meets the eyes.

If you’re serious about setting up an aquarium, you’ll find that there are many things to consider like fish compatibility, tank size, water chemistry, and tank maintenance.

In this guide to freshwater aquariums, I’ll walk you through the steps to set up your first freshwater tank.

By the end of my beginner-friendly guide, you’ll know:

  • Which tank size to pick;
  • What type of equipment you need;
  • How to cycle your aquarium;
  • Which fish to keep;
  • How to clean your aquarium.

Why Start with a Freshwater Aquarium?

If you’re a beginner, I recommend starting with a freshwater tank.

Many beginner aquarists will go into fishkeeping believing that there’s no difference between maintaining a freshwater aquarium and a saltwater aquarium.

I hate to burst any bubbles, but there are significant differences in the maintenance regime of the two.

The reason I recommend starting out with a freshwater aquarium is that freshwater fish are less expensive than their saltwater cousins.

They’re also much hardier, which means they’re more forgiving than saltwater fish. If any problems were to arise in maintenance, freshwater fish are less fragile than saltwater ones.

Saltwater aquariums are more expensive to set up and maintenance is also more precarious. They require additional equipment, special lighting and additional work during water changes.

Therefore, until you get some experience under your belt, I recommend starting with a freshwater tank.

Here’s how to set up your freshwater aquarium in 5 easy-to-follow steps:

1. Picking the Right Tank Size

Sizing the tank correctly is important for the health and wellbeing of your fish.

Larger tanks are also more stable than smaller tanks, so if in doubt, pick the larger tank.

If you already know the type of fish you’re going to keep, check their tank requirements and size your tank accordingly based on the number of fish you want to keep.

Even so, I don’t recommend choosing a tank smaller than 10 gallons, in fact a 20-gallon tank is the best for beginner aquarists.

You can pick out each item for the tank yourself, or you could go with an aquarium kit for beginner aquarists that includes the tank, filters, water conditioner, fish food, and other things you may need.

Buying a kit with everything included can be cheaper than choosing each item separately.

A quick search on Amazon for aquarium kits will return many examples of all-inclusive kits for beginners that ship with everything needed to set up your tank.

Another thing to consider is where exactly are you going to keep your tank.

You don’t want to keep the tank in direct sunlight, so choose a place that gets some natural light but not in excess.

Besides the room, make sure you have a sturdy piece of furniture with a flat surface that can support the weight of the tank along with all the other equipment (filters, lights, etc.).

Cabinets are recommended for larger tank, while any sturdy furniture with a flat surface will do fine for smaller tanks.

2. Getting the Necessary Equipment

If you’re not going to invest in an aquarium kit, you’re going to need to buy all the necessary equipment separately.

This may cost more, but it will also give you the opportunity to hand pick items based on preference and need.

At a minimum, you’re going to need:

Aquarium Filter

The aquarium filter helps remove decaying matter, excess food, fish waste, suspended particles, etc. preventing cloudiness and the accumulation of toxins in the tank.

There are various filter types that are used in aquarium, but the two most common ones are hang on back (HOB) style filters and canister filters.

HOB filters are recommended for smaller tanks, while canister filters are better suited for larger tanks.

Make sure the filter you’re going to buy can process a lot of water and it isn’t too loud.

Water Conditioner

A water conditioner is needed to dechlorinate tap water and detoxify it before adding it to the tank.

Chlorinated tap water is extremely unhealthy for your fish, so removing it along with other contamination issues is the best way to ensure healthy water for your fish.

Some of the most popular water conditioner brands include Kent Detox, Seachem Prime, API tap water conditioner, and Tetra Aqua Safe.

Alternatively, you could buy aquarium water from a fish store or if you have access to filtered water in your home, you can use that provided that your water filter system removes chlorine.

Next, you can start adding the tank substrate.


Check to see which type of gravel your fish like. With some fish it’s not advised to add gravel that’s too coarse because it can damage their bellies (this applies to some bottom dwelling fish).

For your first tank, I don’t recommend going with a sand substrate either. It costs more, and it is more difficult to maintain.

Go with a gravel substrate that’s not as expensive and that’s easier to clean.

Don’t forget to wash the gravel before adding it to the tank. Use dechlorinated water for this too.

The reason you should rinse the gravel is to wash away dust and other impurities and avoid having a cloudy tank for weeks on end.

Rinse the gravel 4 or 5 times until the resulting water is cleaner.

After you’ve cleaned the substrate it’s time to add it to the tank. Create an even base that’s at least half an inch thick.

Air Pump

You’ll also need an air pump that moves the water, so it gets more oxygen. Some fish and decorations also require an air pump.

Air pumps are easy to use and relatively cheap, so generally you won’t have any issues setting it or operating it.

Now that you’re ready setting up the tank, you’ll need to perform the cycling of the tank before you can add the fish to it.

3. Cycling the Tank

Before you think about skipping this step and going ahead to adding your fish, think again!

Cycling the tank is one of the most important steps you can take to create a healthy and stable environment for your fish.

I’m not going to lie to you, this step is often the most difficult part of getting a tank ready for your fish.

It requires a lot of patience, water testing, and some knowledge about water chemistry.

The scope of cycling your tank is to establish a healthy bacterial colony within the tank.

Simply adding your fish in a tank that’s “sterile”, i.e. not cycled, will result in the death of your fish.

Why? Because the tank has no bacteria that can neutralize the toxins that result from fish waste and decaying food matter.

Now that you understand why it’s important to do an aquarium cycle, here is a quick step-by-step guide:

1.  Spiking Up Ammonia Levels

If you add fish to a tank that hasn’t gone to a cycling process, ammonia levels will spike because of the waste fish generate.

This ammonia is highly toxic for you fish, so what you need to do is perform a fishless cycle.

This involves adding small amounts of fish food to the tank just as you would if you would when feeding your fish.

You’ll need to “feed the tank” like this during the course of a few weeks.

Fish food will decompose and release ammonia into the tank.

You’ll need to buy an aquarium test kit to monitor ammonia, nitrite and nitrite levels.

Ammonia levels in your tank will continue to increase until bacteria that can eat ammonia appear.

When these bacteria appear, ammonia levels will subside, and you’ll be able to detect nitrites in the tank.

2.  Monitoring Nitrites

Continue to feed the tank and monitor ammonia and nitrites.

The nitrite stage will follow the same pattern as the ammonia stage – levels will climb, then as nitrite-neutralizing bacteria develop, levels will plummet.

At this point, you can start monitoring for nitrates.

3.  Monitoring Nitrates

Once ammonia and nitrite levels are no longer detectable and you can detect nitrates, it means the cycle is completed.

Of the three chemicals, nitrates are the least toxic for your fish. In low levels, nitrates are not harmful for your fish, but high levels are toxic.

So, you’ll need to perform water changes and clean the tank regularly to keep nitrate levels under control.

4. Adding the Fish

A newly cycled tank is still in the process of stabilizing, so adding all your fish at once will likely throw off the delicate balance you’ve worked so hard to achieve.

For this reason, add one fish at a time and monitor its health for a week or so, if all seems well and good, you can add the next fish.

There are two important things to remember in this stage:

  • Don’t add too many fish at once and don’t overstock the tank;
  • If you’re building a community tank, only add fish that are compatible with each other.

Overstocking a tank is a bad idea. Not only that your fish will not have enough swimming space, they’ll also become sick from all the waste and toxins that are being produced.

Plus, some fish can become aggressive and territorial, which leads to a stressful environment in which they won’t be able to thrive.

For your starter fish, I recommend adding a few hardy fish that can put up with various water conditions and are not very sensitive to mistakes that you may make.

Platies, Mollies and Guppies are great beginner-friendly fish that get along with each other in a community tank.

When creating a community fish, avoid housing fish that are known to be aggressive towards each other or fish that will nip at the fins of other fish.

It goes without saying that adding small fish to a tank with larger fish is also a no-no, since the bigger fish will mistake the smaller ones for food.

Even though some fish are known to get along, it’s still a good idea to monitor tank behavior when building a community tank.

If you notice incompatibilities or aggressive behaviors, remove the fish that are causing trouble.

5. Maintaining the Tank

Tank maintenance should be carried out regularly to keep the tank clean and toxin levels low.

It’s certainly not a fun way to pass the time, but it’s necessary to keep your fish healthy and your tank clean.

What does tank maintenance involve?

Carrying out maintenance on your tank means performing regular water changes, removing dead plants, excess food, vacuuming the gravel, and removing algae from the surfaces within the tank.

The tools that you’ll be needing to clean your tank:

  • 5-gallon bucket;
  • Fish net;
  • Algae magnet or scrub;
  • Gravel vacuum.

You’ll need the bucket for the water you’ll be siphoning out during water changes. Ideally, you should perform weekly 10-15% water changes.

If you skip a week, it’s not the end of the world, but don’t forget to at least monitor ammonia, nitrite and nitrate levels.

Use the gravel vacuum to remove leftover food and debris from the gravel. Along with water changes, this will reduce nitrate levels in the tank and keep your fish healthy.

Water changes also replenish the water with nutrients and dilutes any harmful substances.

Use the fish net to remove any dead plants or fish and use the algae scrub to clean the glass surfaces and other tank decorations.

Cleaning the tank also prevents algae blooms, which if left untreated will take over the entire tank.

Before you add the new water, make sure it’s dechlorinated and at the temperature required for your aquarium.

Use the bucket with the siphoned water to give the filter a good rinse.

Next, I’m going to discuss some pitfalls to avoid when setting up a Freshwater Aquarium.

Rookie Mistakes to Avoid When Starting an Aquarium

As a novice, the set-up of an aquarium can be challenging. There are many points of failures, which makes things all the more difficult for the inexperienced aquarist.

Let’s see which the most common aquarium mistakes are and how you can avoid them:

1. Adding Your Fish Before the Nitrogen Cycle is Completed

Like many mistakes that I’m going to discuss, this too stems from a lack of understanding of the nitrogen cycle.

Beginners will usually go one of two ways – they’ll either ignore the cycle completely and hope for the best, or they’ll start out well but lose patience underway.

It can take 6 to 8 weeks for the nitrogen cycle to complete.

So, if you don’t have the patience to regularly feed an empty tank and regularly monitor water parameters, maybe you should reconsider fishkeeping as a hobby.

Even if you’ve chosen hardy fish as your starter fish, you’re still going to expose them to toxins, which will eventually reflect in their health.

Once you’ve started with the nitrogen cycle, have patience and keep going until you see results.

2. Getting a Tank That’s Too Small

While starting with only a few fish is not a bad idea, starting with a teeny-tiny tank equals setting yourself up for disaster.

Why? Because in a small tank there’s no room for error.

In small tanks, a small mistake can have huge consequences and immediately throw off water parameters.

The larger the tank, the smaller the chance of mistakes having a huge impact.

Therefore, until you get some more experience, it’s best to begin with a 20-gallon tank.

3. Overstocking the Aquarium

This is another mistake that has its root in not understanding how many fish a tank can comfortably house.

Adding too many fish will make it impossible to maintain optimal water parameters.

The 1 gallon per 1 inch of fish rule that I’ve seen recommended in many fishkeeping guides is not the best measure.

Instead take your tank’s net capacity (the one that results after adding the gravel and decorations) and multiply it by 75%.

The resulting number will tell you the total length of mature fish you can keep in the tank.

Let’s say that your tank’s net capacity is 16 gallons. Multiply this by 75%, and you’ll get 12, which means you can keep a total of 12 inches of mature fish in your tank.

4. Insufficient Filtration

Getting a cheap filter system that barely turns the water in your tank 2 times per hour is not good enough.

Find one that turns the water at least 3 to 4 times per hour. If in doubt, it’s better to oversize the filter.

5. Lack of Water Testing

Get a water testing kit as soon as you’re planning on adding water to your tank. The water testing kit will help you monitor water parameters during the nitrogen cycle and beyond.

After you complete the nitrogen cycle, you’ll still need to monitor toxin levels to see if there are any changes you should be aware of.

Problems may be brewing without any noticeable signs, so testing water parameters is the only way to know for sure is something is wrong before your fish suddenly get sick.

6. Not Recognizing the Signs of Fish Poisoning

Another extremely common mistake is beginners accidental poisoning their fish by not cleaning the tank and not performing any water changes.

When this happens, your fish:

  • become lethargic;
  • lose their appetite;
  • sink to the bottom of the tank;
  • may come up to the surface of the tank to gulp for air;
  • show signs of inflammation on their eyes, gills or anus.

Of course, all these can be avoided with proper care and maintenance.

7. Overfeeding

Just because your fish will keep on eating after you’ve fed them the recommended amount of food, it doesn’t mean they’re always hungry.

In fact, they can go a few days without food without problems. In fact, when you’re starting the tank, it’s best if you only feed them every other day to avoid creating excess waste in the tank.

As a rule, feed your fish once a day with an amount they can consume in five minutes.

Each fish species has their own eating habits, so make sure to adjust this rule whenever necessary.

8. Keeping Incompatible Fish

Beginner will often select fish based on their personal preferences without much regard to water conditions and compatibility.

When choosing tank mates, make sure fish aren’t from species that are known to show aggressivity towards each other or that prefer very different water conditions.

Always research the keeping requirements of the fish species you’re planning on housing together to make sure they like the same water conditions and get along with each other.

9. Slacking on Water Changes

Just like overfeeding and overstocking the tank, missing out on water changes throws off the balance in the tank, allowing toxins to build up and increase their susceptibility to diseases.

You can’t go wrong with performing weekly 10-15% water changes that will physically remove excess waste and dilute toxins.

10. Not Knowing How to Treat Algae

Algae blooms are another issue that not only beginners, but even expert aquarists can struggle with.

Therefore, I recommend that you educate yourself on the various algae types and ways to remove them, but also on ways to prevent algae from getting out of control in your tank.

Regular tank cleaning, monitoring water parameters, and ensuring proper light conditions are some of the best ways to prevent algae blooms in your aquarium.

As you can see most mistakes that beginners do while setting up a freshwater aquarium happen as a result of:

  • Not understanding the importance of the nitrogen cycle;
  • Now knowing how to introduce fish in the aquarium;
  • Slacking on tank maintenance.

Being strict about these matters is the best way to prevent issues in your tank.

Final Thoughts

Now that you’re more in the know about how to setup a freshwater aquarium, I hope you don’t feel discouraged from starting out with your first tank.

There’s certainly a learning curve when it comes to fish husbandry, but if you follow the steps described in my guide and avoid the mistakes uninformed beginners make, I am sure you’ll manage to setup your first aquarium and enjoy it for years to come.


Featured Image:

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
Questions and Answers
Cynthia Morales September 7, 2020 Reply

Not knowing anything about nitrates, do you have any information that I can read in regards to how to read on where these levels should be at for maintains a healthy tank. By the way thank you for all the information you provided in this article

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