Can You Keep Your Fish Tank Outside?

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Setting up the ideal aquatic environment takes time, commitment, knowledge, and experience. A lot of aspects play a vital role in the system’s stability, including the aquarium’s location.

Today, we will discuss the difference between indoor and outdoor tanks and what to know if you’re going for an outdoor one.

Indoor aquariums are pretty much the norm, but many people will go for outdoor ones, especially when it comes to larger aquariums.

However, as you will see, outdoor tanks come with unique challenges that require quite the brainstorming to overcome.

5 Things to Consider When Keeping Aquarium Outside

There are a few things to consider when keeping a fish tank outside such as the placement of the tank, outside temperature, fish species you are keeping, the size of the tank and potential predators. Now, let’s see each one in more detail:

1. Placement of Your Tank

Your tank’s placement makes all the difference in the world. While there are many aspects to discuss here, such as aquarium stability, wind exposure, or weather vulnerabilities, we will instead focus on the most impactful one – sunlight. Fish don’t need too much light, to begin with.

After all, most aquarium fish live in medium-to-low light conditions. Most aquarists use brighter lights for themselves to be able to see the fish better, not for the fish themselves.

Placing your aquarium under direct sunlight will not only stress out the fish but also promote algae overgrowth.

Algae thrive in bright light conditions and take over their habitat quickly when the ideal circumstances arise. You can mitigate the algae’s impact by adding live plants to the tank.

These will take up space and consume the very nutrients that algae would prefer. This will keep algae at bay, but not if you don’t manage your light conditions.

If light intensity or duration are inadequate, the algae will take over, flood the habitat, cover the plants, and restrict their access to sunlight.

This could mean death for your plants since they can no longer perform photosynthesis.

Fish may begin to die, too, as they get tangled in the compact mass of hair algae, creating genuine webs in the water.

To prevent this, you should always place your aquarium in a cool and safe area, protected by direct sunlight, powerful winds, rain, and other weather conditions.

This isn’t enough to protect your aquarium against algae, but it’s a good start.

2. Temperature Changes

All tank fish require certain temperatures to remain healthy and active over time. Most warm water fish will thrive in temperatures around 72 to 82 F with some variations occasionally.

Temperature fluctuations aren’t necessarily a problem since all fish can adapt to temperature shifts.

It’s normal for the water’s temperature to change depending on the time of day.

The problem is with aggressive or repeated temperature changes that could disrupt the system’s stability.

Your fish may experience temperature shock, causing them to display signs of stress as a result. These include lethargy, erratic swimming, lack of appetite, rapid breathing, etc.

If the tank water is too cold, your fish will swim less in an attempt to preserve their energy. If the temperature doesn’t get back to normal, they may experience temperature shock, hypothermia, and death.

Or if the water grows too hot, your fish will begin to suffocate since the hotter the water gets, the faster the oxygen levels will drop. Naturally, outdoor tanks experience wilder temperature shifts than indoor ones.

To fix the problem, keep the tank safe from direct sunlight and have a heater in place. Especially if you reside in a zone where the temperature varies drastically between day and night.

Plus, you should always consider your geographical positioning before setting up an outdoor tank. If the environmental temperature changes drastically from one season to another, you should consider moving the tank back inside as the weather cools off.

Guppies, for instance, are tropical fish, so they cannot withstand temperatures lower than 70 F. Sure, they can survive it for a while, but they will eventually face health problems.

The colder the water gets, the more likely your guppies will experience problems with their immune system. The same goes for all tropical fish.

3. Fish Species

There are a variety of fish fit for outdoor tanks and ponds and an equal number of fish that are not about that life. Goldfish, koi, Hi-fin sharks, and other carps are great for outdoor use.

These are adaptable and hardy fish species capable of withstanding the harsher conditions of Mother Nature.

Guppies, plecos, and pretty much any tropical fish are to be kept inside. The main concern here is, as you may have guessed already, temperature. Tropical fish require stable temperatures and warmer waters.

Keeping them outside is possible but unlikely since you can’t really control the water’s temperature as you can for indoor tanks.

So, choose your fish species carefully to prevent a tragedy along the way.

4. Size of the Tank

This typically boils down to personal preference, but consider this: larger tanks are generally more stable. Smaller tanks will experience more aggressive temperature changes and require more extensive cleaning and maintenance.

So, you should consider at least 75 gallons for your outdoor tank. This is enough to maintain the system’s stability and provide your fish with sufficient space to remain happy and healthy.

The tank’s size also comes into play when it comes to the aesthetic factor. Most people keep their outdoor fish in large ponds, making them easier to clean and maintain.

If you’re going for an aquarium instead, consider finding the ideal spot from the get-go.

This will save you from having to relocate the aquarium in case the environmental conditions don’t live up to your expectations.

5. Predators

You may not have considered this one, but it’s a legitimate threat. Outdoor aquariums and ponds are semi-open environments since they have open contact with nature.

This opens the door for a variety of predators which will take notice of your fish. It’s not uncommon for birds, small reptiles, and even mammals to hunt pond fish when no one’s looking.

Housing the fish in an outdoor tank will arguably make them even more vulnerable. At least a pond is generally darker, providing the fish with some shelter.

Especially if you have a ton of live plants for a plus of cover.

A tank, however, is a flashier setting with transparent walls. The existent live plants won’t do much to cover your fish’s profile. If anything, they will highlight them since live plants boost the fish’s coloring and behavior.

So, always keep your guard up for potential predators threatening your fish’s safety. Once they’ve caught your fish’s scent, they will remain in the area and return as often as needed to attack them relentlessly.

You can deter potential predators by placing a lid on the tank. Make sure it has holes in it to ensure optimal oxygenation and prevent dangerous CO2 accumulation.

What Fish Can Live in Outdoor Tanks?

With the right preparation and awareness, I would say that any fish can live in an outdoor tank. Including guppies and other tropical fish in need of more controlled environmental conditions.

Your main concern here is temperature. So long as temperatures are stable, your fish will thrive, no matter where the tank is located.

I would say that goldfish and koi are the kings of outdoor setups. These are adaptable and hardy but require a lot of space and intense regular cleaning. They are famous for producing impressive amounts of waste, which can overwhelm the environment quickly.

They also require deeper waters and more swimming space than smaller species, more adapted to indoor settings.

Mollies, swordtails, gouramis, and other similar fish can easily adapt to an outdoor life, provided their aquarium conditions are stable. So, it all depends on your level of involvement and how well you optimize their environment.

Don’t Let Water Freeze in a Glass Tank!

Invest in a heater if you live in a geographical area with vast temperature differences between night and day. Do so even if your fish are cold-water creatures accustomed to colder environments.

The water in the tank can get very cold very fast under the right conditions. This can lead to hypothermia and kill your fish rather rapidly.

I recommend testing things out beforehand. Set up the aquarium, add the plants and decorations, and keep the tank outside for several days to a week before adding the fish.

Monitor temperature changes during this time and notice how they fluctuate depending on the time of day.

This will highlight the best way to set up the heater to ensure optimal conditions and prevent extreme temperature fluctuations.


Setting up an outdoor tank isn’t a much different experience than setting up an indoor one. It all comes down to becoming aware of the differences between the 2 setups and adapting accordingly.

Needless to say, your fish will thrive in an outdoor setup with the proper support and assistance along the way.

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.
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