Fish for fish tanks: Everything you need to know.

Many people love the aquatic world and love fish for fish tanks. And it’s  an aquarium in addition to being a beautiful space to see how the fishes’ life develops as well as the interaction between several species.

But an aquarium should not be taken lightly; It must be remembered that these are living beings that we care for and deserve all our respect, as well as the necessary care so that their life passes in optimal conditions.

With this article, we want to show you some of the different types of fish that you can breed, whether freshwater or saltwater fish, as well as some indications on what to do if they get sick.

Basic Considerations before having fish for fish tanks.


The aquariums’ world of is so extensive that it could overwhelm you if you’re just getting started.

Most likely, you are impatient and just want to fill a tank with water and put many fish for fish tanks to see them swim and interact with each other.

However, most likely this behavior will only lead to the death of all your pets.

Before you start selecting the fish that you want to have and start your own aquarium, there are some details and tips that you should take into account to provide the best space and environment for your new pets.

10 mistakes that most beginners make with their first aquarium

Location, location, location.

It seems like a real estate motto, but even if you don’t believe it in the case of fish for fish tanks, the fish tank location is as important as the fishes’ diet , since several natural factors such as light or wind affect the life and development of animals.

The first thing you should consider is to place your aquarium in a key place where sunlight does not directly affect it.

Moreover, it’s also advisable to avoid air currents coming from windows or heating equipment, since the water temperature could rise or fall to risky levels for the fish causing unnecessary stress.

Maintenance Equipment.

So that your fish for fish tanks have an optimal life, certain equipment such as water heater, cleaning filters and UV lamps are necessary. Before introducing fish for fish tanks in their new home, make sure that these devices work correctly for a couple of days.

Let’s learn about each one of them.

What are aquarium filters?

If you are starting with aquarium, you will be wondering about the importance of aquarium filters and if they are really so necessary.

The filters are mechanisms that have the task of filtering the aquarium water, to eliminate the impurities they may contain.

They take the water from the aquarium and make it pass through a series of filtering materials, and once biologically purified, reintroduce it into the aquarium.

The most important part of the filters is the pump, which is the one that sucks the water from the aquarium, forces it to pass through the filters and returns it to the aquarium.

Depending on their position, the aquarium filters are divided into two large groups, exterior and interior:

√ External filters are placed outside the aquarium. They are indicated for large aquariums.

√ The filters for indoor aquarium are those that go inside the aquarium. They are usually mounted in small aquariums.

Why are aquarium filters so important?

Stagnant water deteriorates if it’s not filtered and oxygenated.  In addition, we must add the deterioration caused by the fish, which leave traces of food and their own physiological waste.

In a natural environment, the physiological and food remains produced by the fish, decompose and end up being processed by nature without any problem.

But in an aquarium this doesn’t. The amount of organic remains far exceeds the limits that the aquarium can process biologically; we must provide the aquarium with a filtration system, so that the water quality is assured and the fishes’ life is not in danger.

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UV Lamps

UV aquarium lamps are very useful for removing suspended algae, as well as preventing and treating some of the common diseases in fresh and salt water aquariums. 

Basically, ultraviolet light lamps «kill» all kinds of bacteria, virus or algae cells. It can kill any type of bacteria, including nitrifiers so they are very useful for the aquarium cleaning process…

How do ultraviolet lamps work in the aquarium?

Ultraviolet lamps produce ultraviolet radiation or UV radiation, which one of its main applications is sterilization.

At certain wavelengths, it damages the DNA of the microorganisms present in the aquarium water, such as bacteria or viruses, without leaving any residue and preventing them from reproducing.

The aquarium’s ultraviolet lights are usually isolated, so that only water is affected by its radiation. It’s  important to remember that we should not look directly at the light, since we could be affected.


The best way to control the aquarium’s temperature is by using a heater. The functions that this small device has are:

Keep the water at a constant temperature.

√ Allow the survival of hot water fish.

Promote the growth of the bacterial population that allows biological filtration

In the same way you should consider the levels of pH, salinity and hardness according to the needs of your fish for fish tanks, making sure that they are as similar as possible to the water of their natural environment.

Let’s learn a little more about this.

Water quality

The Aquarium water is the fundamental element for aquarium hobby. Given this absolute truth, it’s necessary to know the water’s main characteristics of and how they can affect the members of the aquarium.

All the fresh water that reaches our homes has only one origin: rainwater.

It may seem that this water is the most suitable for an aquarium due to its apparent cleanliness, but it’s not so, especially in large cities where there is huge air pollution and rainwater is loaded with all of them.

The water that maintains more stable characteristics and better quality is the tap water.

Water composition

Water is the result of the combination of two gases, hydrogen and oxygen. The aquarium water’s quality, as well as its chemical composition, are fundamental aspects for all living things inside it.

For the care of fish and plants, we must pay special attention to the following characteristics: pH, hardness, conductance and resistance. We must know what they are, how they affect the aquarium and how we can control them.


The acronym pH comes from «hydrogen potential». The water’s acidity or alkalinity is expressed by pH and varies between 0 and 14, with “0” being the maximum acidity and a pH of 14 means that we are facing a very alkaline water. PH 7 is neutral.

The pH of the aquarium water should be measured every week to determine the water’s quality

Inland fish require a pH between 6.5 and 8.5, while Amazonian fish that live in sewage waters prefer soft water, between 6 and 7; East African species prefer a pH between 7.5 and 8.

The best and easiest way for measuring the aquarium’s pH is the colorimetric method in which you’ll employ a liquid solution, contained in a pH analysis kit.

In this Kit we will find a color wheel and a reagent. Then, to determine the aquarium’s pH, the color of the water’s mixture with the reagent is compared with the colors of the wheel.


Water hardness measures the amount of calcium and magnesium salts, contained in the aquarium water. 

 There are several acronyms to express this variable being the most common the German grades, dH which is measured in milligrams.

Dh tells us the amount of dissolved salts per liter of water and the higher the dH, the harder or alkaline the water. Hard water will have a high pH, ​​and a soft water should be more acidic.

We can measure the hardness using a colorimetric method that uses reagents, to determine the water’s hardness depending on whether they are dyed in one color or another.

Limestone or carbonate hardness

Almost all waters contain bicarbonates, which are measured in degrees KH. The presence of bicarbonates influences the regulation of pH, and as a consequence, the health and development of the organisms inside the aquarium.

A KH between 5º and 18º is recommended for most inland fish, while fish from large African lakes need higher carbonated hardnesses, and marine fish need KH values ​​to be between 15º and 18º.

Conductivity and water resistivity

The conductivity and resistivity of water is based on the principle of circulation of electric current between two electrodes, and allows to determining the mineralization of water.

Hard water more easily transmits the electric current, because it contains a large concentration of minerals.

The resistance is exactly the inverse measure, since hard and highly mineralized water (i.e. sea water,) has a very low resistance, so that the current easily passes from one electrode to another.

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Aquarium Cycling

Cycling is a process whereby we get bacteria colonies to settle in the aquarium, to help us with the nitrogen cycle. The bacteria that settle in the aquarium are part of the water filtration system.

Thanks to its beneficial effects, in a completely natural way some of the aquarium’s waste is degraded, maintaining the natural balance of the ecosystem.

What happens if I don’t cycle the aquarium?

If you don’t do the aquarium cycling and just buy your new aquarium to introduce fish, they’ll probably end up intoxicated and die.

In the best case, they can suffer all kinds of diseases and especially stress, because they are in an environment without sufficient quality to survive.

How to start cycling?

The first thing we have to do to start cycling the aquarium is “just to start it”.  First of all, we will have to have decided what type of aquarium we would like to have, to then introduce the elements that will be part: substrate, decoration … everything but fish, and in the first phase we won’t introduce plants either.

Of course we shouldn’t forget the aquarium’s filter, which is very important for the cycling process to be correct and the first bacteria to appear.

You have to connect everything you need to reproduce the chosen biotope: heaters and lights, although these will not start until we get the first plants.

How long does the aquarium cycle take to complete?

The time it takes for the cycling process to complete varies depending on the type of aquarium.

For a freshwater aquarium it’s likely that with one month it will be enough, while in a marine aquarium it takes between two and three months to get all the parameters stabilized.

How to know if the cycling process is over?

In the first two or three days after introducing the water into the aquarium, we will observe that the water is cloudy due to the effect of filtering and the various suspended materials that come from the substrate.

Subsequently, the water begins to rinse until it’s completely transparent. We can think that the process is over and that we can start introducing fish … No!

Throughout the process we must periodically monitor the water quality, using the different tests available for this purpose.

Once we get rid of the ammonia and the nitrites go down to zero levels, we can say that the process is over and we can start introducing fish.

The nitrogen cycle inside the aquarium

Nitrogen, as a chemical element, is part of the tissues of animals and plants, and obviously, is present in the organic substances that are released from them: fish carcasses, urine, feces and plant debris.

These organic materials are transformed into ammonia (NH3), a very toxic compound and ammonia (NH4 +), one hundred times less toxic.

In the presence of oxygen, aerobic bacteria transform ammonia into nitrites (NO2), dangerous for fish and nitrates (NO3), much less toxic. This process is known as nitrification.

We can positively influence this process, so that it’s most beneficial for the aquarium and fish.

One way to favor the development of aerobic bacteria is the installation of a porous substrate, through which water circulates easily providing oxygen to the bacteria.

If the amount of oxygen is low, aerobic bacteria will be replaced by another type of bacteria, anaerobes, which reduce nitrates to nitrites, increasing the accumulation of ammoniacal compounds, harmful to aquarium life.

Another way to favor the nitrogen cycle is the frequent and regular change of aquarium water. In any case, the worst is the concentration of nitrites, which in no case should exceed 0.21 milligrams per liter.

One of the reasons why you should wait at least two weeks to introduce fish into the aquarium is that you need the bacterial colonies to appear since they facilitate the nitrogen process.

Tips to improve nitrification in the aquarium

Feed the fish the food they are able to consume in a few minutes, so that food debris is reduced to      a minimum, which can then be broken down.

Quickly remove food debris and organic waste from the bottom.

Monitor the filters’ operation adapting them to the number or type of fish in the aquarium.

Provide support for the development of bacteria.

 √ Renew part of the aquarium water every week.

Monitor the good growth of aquarium plants.

 √ Perform periodic measurements of the concentrations of ammonium, nitrites, nitrates and pH.

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Amount of Fish

The large and densely populated aquariums that we can watch on TV shows or movies are beautiful. However, unless we have a total time or money availability for someone to take care of our pets, it’s better to have few fish.

In these cases of aquarium population it’s better to think of “less is more”, since overpopulating our water tank can cause the fish to become stressed and even when they are very submissive animals they will begin a terrible battle for territory and food .

Also when you buy fish for fish tanks, it’s common to buy specimens that can grow a lot according to the species and need more swimming space than others.

Therefore, populating our aquarium little by little is the best way to create our small community..

Compatibility with other fish.

All fish for fish tanks have a particular beauty, but this doesn’t mean that everyone gets along. There are species of fish that are really aggressive so they should be kept alone, such as the betta or Siamese fighter fish , which constantly harasses the other fish in the aquarium, even those of its own species.

There is also the possibility that without knowing you introduce carnivorous fish that will devour the smallest specimens, which can be just terrible.

In other very common cases, people acquire only one specimen of a fish that needs to live in schools of at least 6 individuals.

For these reasons it’s important that you know the personality of your fish for fish tanks, in addition to making sure the type of relationship they could have with the other species that you already have at home. We invite you to read our article Barb fish to learn about the behavior of these striking fish for fish tanks

How to introduce a new fish.

Changing the position of the decoration can be of great help so that the new fish are better integrated into the group, as can happen in the case of having cichlid fish in your aquarium.

In this scenario, you will surely have some dominant males that can haunt new males for competing for the territory, but the change in decoration will lead to disorientation in old fish. This will make the males don’t   fight each other and the new fish for fish tank can adapt better.

Now, breathe, relax and enjoy

Freshwater Fish for Fish Tanks

Before you start having your fish tank full of specimens, it’s important that you know the particular needs of each fish to provide them with the best living conditions.

It’s also vital that you know what their natural habitat is so you don’t go through the pain of watching your pets die.

Below is a small list of fish for fish tanks easier to care for and the most common.

Generally freshwater fish are the first choice of beginners in the aquarium because of their easy care and maintenance as well as their great adaptability to new environments.

Molly Fish

Molly fish, or just mollies, are freshwater fish from the genus Poecilia, in the Poeciliidae family.

All the species in this genus are mollies except for the Endler’s livebearer. They’re family of guppy and platy fish.

Main Characteristics

Adult Molly can measure between 5 and 12 centimeters, depending on whether they are male or female. They have an elongated body, with a slightly pointed head and mouth, where we find well sharp teeth. Their fins have soft radii.

In terms of body color it’s very diverse, as a consequence of the different crosses made by aquarists.

In their natural state Molly Fish tend to be black and speckled in yellow, however for sale we find Molly black, orange, marbled, white, red, gold,…

The amount is wide and from time to time, we are surprised with a new hybrid of Molly fish.

To distinguish them from the Guppy, the Mollys have a thicker body and their fins are not elongated, rather rounded.

An important aspect to highlight from molly fish is their marked sexual dimorphism, which makes it easy to differentiate the female from the male.

One of these aspects is the size, since males usually measure up to 6 centimeters in length, while larger females can reach 10 centimeters. In addition to this, males have a gonopodium in their anal fin which they use to hook and mate with the female. We invite you to read our article the anatomy of fish to learn about this interesting topic

Care inaquarium.

The first thing you should know is that molly fish reproduce very quickly, and a male without activity constantly harasses a female even causing death. So, if you want to have several specimens it’s suggested that you put 3 to 4 females per male.

When the female has received the sperm pack incubates the eggs inside her body for about 30 days then releasing her already formed offspring: around 60 although sometimes they can be up to 200.

It’s important that the little ones have enough algae to hide from larger fish, (including the mother) so as not to be devoured.

On the other hand, and in the same way than midas Cichlids   mollies are omnivorous animals, that is, they can eat everything. However, the ideal is to feed them with a rich diet of plant origin that can be supplemented with mosquito larvae and commercial food in scales.

Moreover, they deserve enough space to swim, so a large tank of at least 50 liters will be ideal for  them.

Finally, it’s important to point out that Mollies are docile and sociable so they will get along with almost any species. If you provide the necessary care mollies can live between 2 and 3 years.

Let’s keep learning

Guppy fish

Guppy fish are fish for fish tanks that are also very easy to care for and maintain, so they are ideal for those new fans of the aquatic world.

They belong to the Poeciliidae family, with the scientific name of poecilia reticulata, although they are popularly known as millionfish and rainbow fish.


Guppy fish have a quite remarkable sexual dimorphism, the male being smaller and with brighter and prettier colors in his tail than the female.

In addition to this, the female has a black spot in the lower part of her body that becomes larger and indicates the proximity of the birth during the incubation period.

Even in some cases small spots, which are the eyes of small fry, can be seen through the spot.

Care in the aquarium.

These fish for fish tanks are omnivorous, so their diet should be based on protein-rich foods that nourish them very well, such as artemia, water flea, mosquito larva or tubifex.

You can also give them small pieces of previously cooked vegetables, and they really love peas.

Their diet can be supplemented with commercial food in the form of granules and scales.

The aquarium’s size must be at least 50 liters so that they can move comfortably and without restrictions.

In addition the water must be at a temperature between 22 to 28º, where the ideal would be 25º C. Remember that as in the previous case if you want to place several specimens you must enter a minimum of 3 females for each male.

You can add enough live vegetation to the aquarium to give your fish for fish tanks an ideal environment to rest, in addition to serving the fry to shelter from their parents and other large fish that could eat them.

Let’s watch them


They belong to the Cyprinidae family in the order of cypriniformes; their scientific name being Danio Rerio.  This is a species for small fish tanks, which seldom exceed 5 centimeters in length.

Yet, despite zebra fish’s small size they need a large tank, of at least 100 liters, because it’s a species accustomed to living in shoals and merits placing at least 6 individuals with greater preponderance of females.

So, it’s very important to highlight that if you place a single specimen inside the aquarium it will die of sadness for loneliness.

The advantage of these fish for fish tanks is that they are omnivorous and can feed directly on the surface, for this reason you can feed them with mosquito larvae, small terrestrial insects and even small spiders.

Supplement their diet with commercial food in the form of scales or granules, but make sure it’s floating, since zebrafish don’t eat from the bottom.

But don’t stress out since once they are satisfied it will be easier to clean the leftover food. We invite to read our article betta fish  to learn  about other striking freshwater fish for fish tanks.

Let’s watch and learn

Salt Water Fish for Fish tanks.

Like freshwater fish, saltwater fish have many impressive and striking colors even in some cases more colorful and elegant, but also merit prior knowledge of the species before introducing them into the aquarium .

As in the previous case, you should know if they are cold or hot water as well as their customs and behavior before other species to avoid confrontations, especially if you have a community aquarium.

These fish for fish tanks need a degree of salinity in the water that must be constantly measured with a hydrometer, especially after cleaning and changing water.

But don’t think you can use edible salt from the one you find in the supermarket, because it has a lot of iodine that can be fatal for your pets.

You should use special sea salt sold in pet stores. Generally the salinity degree should be maintained between 1020 and 1023.


Belonging to the Pomacentridae family, in the order of the Perciforms, Damselfishes are one of the best fish for fish tanks for beginners due to their resistance to changes in environmental conditions and their adaptability to them.

They can have a length of 7 centimeters to 36 centimeters, although in cases of being in aquariums they are unlikely to grow so much.


Duringng younghood, damselfishes tend to be very peaceful fish but when they reach maturity the males become aggressive with each other,.So you must place a male and several females in the aquarium.

In their natural habitat they live in coral reefs where they can camouflage with the environment to escape from predators.

Although in an aquarium they won’t have this problem it’s good to place reefs as decoration that they can also use to rest.

It’s also important that the water temperature is maintained at 25 ° C. Damselfishes are omnivorous fish that you can feed with algae, small crustaceans, fish food in the form of flakes, cooked vegetables and small pieces of meat or frozen fish.


This famous fish became popular because of the animated movie «Finding Nemo», which made many people fall in love with their colors and personality since it’s certainly an exotic aquatic creature.

Despite being  very resistant to some water changes, it’s necessary to provide them with adequate space and conditions to make them feel comfortable.

The aquarium should be large, since although the clownfish is small it needs a lot of space to swim. In addition to that it reproduces fast and you will need space for the young.

A good tank must have a minimum capacity of 150 liters to house a pair of clownfish. Now in case you have about 5 specimens, you will need a 450 liter tank.

The water temperature should  be maintained between 24 and 27º C. To better recreate the clownfish’s natural environment  you can include an anemone, which they will use as a house and shelter against predators.

Emperor Angelfish.

This fish for fish tanks is a bit more complicated to care for, and deserves an owner who is already accustomed to maintaining an aquarium and can provide adequate care.  So it’s not recommended for beginners.

To keep them with ease it’s necessary to have a large aquarium, with a minimum capacity of 378 liters of water for only one specimen.

So, if you want to have a pair of emperor angelfish you need to double the tank’s size and capacity although they are usually lonely creatures.

The aquarium should have many rocks and caves where they can hide, although it’s not recommended to place coral reef as they will peck it and in some cases they can be hurt.

To feed them you can use artemia, mysis or commercial food in the form of scales or pellets. You can also offer mussels, shrimp, squid and spinach to complement and vary their menu.

If you take care of them properly emperor angel fish can have a life expectancy of up to 10 years.

We invite you to read our article emperor angel fish to learn more about this species…

let’s meet them


Common Diseases and their cures.

Fish for fish tanks also get sick, but they do so especially when the care we provide them is not adequatethe proper one.

To prevent your fish from getting sick and even dying, make sure you keep the water levels stable as well as the temperature, as sudden changes could trigger serious symptoms.

Similarly, you must constantly clean the water tank at least once a week and change the water (between 20 and 30%) every time you clean it.

Don’t think that having a small aquarium demeans less attention; on the contrary it needs a more strict cleaning ritual since it’s easier to get dirty.

On the other hand, never use soap or a chemical to clean the internal walls of the aquarium since it could be deadly for your fish.

 Moreover, follow very well the instructions of how much chlorine you should add to the water according to the amount of liters.

It’s common that people when trying to have an extremely clean environment exceed the amount of chlorine they should add to the water and the fish suffer poisoning.

On the other hand, take good care of your fish’s diet, which must be varied and of quality, since you could cause constipation that will become visible in the fish by having a bulky abdomen and poor mobility.

There may also be other less common diseases caused by fungi, parasites or viruses that manifest in their skin and at the same time their peaceful attitude changes by a restless and desperate behavior. In many cases leaning on stones and plants to scratch.

If this happens it’s important that you consult an experienced veterinarian who can offer you the appropriate medicines and recommendations.

Fish for cleaning fish tanks.

There are kinds of fish for fish tanks that will be very useful, in addition to that they adapt very well to the interaction with other fish; they are commonly called  cleaning fish.

These creatures are characterized by eating decomposing organic matter or in some cases the algae that occur in the glass of fish tanks.

With their integration into the aquarium your cleaning load can be lightened a bit, although you should never neglect it.


This fish has long mustaches on each side of its mouth that it uses to dig into the ground in search of food debris or debris found at the bottom of the aquarium, so they will literally spend the day sweeping and cleaning your aquarium.

But don’t trust, the catfish can also eat smaller fish if it doesn’t have enough food, so don’t forget to feed it like the rest of the fish for fish tanks.

Its diet may be based on some pieces of shrimp and frozen fish as well as commercial food.

They are resistant and adaptable to life in captivity and don’t grow much, so they don’t exceed 5 to 6 centimeters in length.

When acquiring this pet you must make sure what its natural habitat is, since there are freshwater species and saltwater species.

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