Upside Down Fish Tank – The Ultimate Guide To Building Your Own

Have you ever stared at your aquarium and wished you could add a whole new dimension to your hobby? You have likely seen those mesmerizing videos of fish swimming above the waterline in what looks like a magic trick.

It is not magic—it is physics, and creating an upside down fish tank is one of the most rewarding DIY projects you can undertake. I have spent years experimenting with different setups at Aquifarm, and I can tell you that this specific project always turns heads.

In this guide, I will walk you through exactly how to build and maintain an upside down fish tank safely. Whether you are a seasoned pro or a curious beginner, you will learn the secrets to keeping your fish happy in their new “penthouse” view.

Understanding the Science of the Upside Down Fish Tank

The first thing most people ask when they see an upside down fish tank (often called a fish tower or vacuum tank) is: “Why doesn’t the water fall out?” It feels like it defies gravity, but it actually relies on atmospheric pressure.

When you submerge a container, fill it with water, and lift it while the opening remains underwater, the pressure of the air outside the tank pushes down on the main water surface. This pressure is strong enough to hold the water inside the elevated container because there is no air inside to push it back down.

As long as the “mouth” of your inverted tank remains below the water level of the main aquarium, the water will stay put. This creates a vacuum effect that allows your fish to swim up into a column of water that sits high above the rest of the tank.

Why Every Aquarist Should Try This

Beyond the “cool factor,” these setups offer a unique perspective on your pets. You get to see your fish from the side in a way that traditional tanks often obscure, especially if you have a rimless setup.

It also increases the total water volume of your system. More water means greater stability in terms of temperature and water chemistry, which is always a win for the health of your aquatic life.

Essential Materials for a Successful Build

Before you start, you need to gather the right supplies. Using the wrong materials can lead to structural failure, which is a nightmare for any hobbyist. Safety and stability are our top priorities here.

You will need a clear container for the “tower” portion. While glass is beautiful and scratch-resistant, acrylic is often preferred for beginners because it is lighter and easier to handle during the installation process.

The Support Structure

The tower cannot simply float; it needs a solid base. You can use PVC pipes, acrylic rods, or even stackable aquarium-safe rocks to create a platform. The goal is to ensure the tower is elevated enough for fish to swim under, but stable enough not to tip.

Tools for the Vacuum

To get the water into the tower, you will need a manual siphon pump or a small piece of airline tubing. Some hobbyists even use a wet/dry vacuum for larger builds, but for most home setups, a simple tube and some lung power (or a pump) will do the trick.

Step-by-Step Guide to Setting Up Your Tower

Setting up your upside down fish tank requires patience. Do not rush the process, as ensuring a perfect seal and stable positioning is critical for the long-term success of the project.

First, prepare your main aquarium. Ensure it is level and that the glass can handle the extra weight of the water-filled tower. Remember, water is heavy—about 8.34 pounds per gallon!

Preparing the Tower

1. Clean your tower container thoroughly with vinegar and water. Never use soap, as residues can be fatal to fish and shrimp.
2. Place your support structure (like aquarium-safe bricks or a custom acrylic stand) inside the main tank where you want the tower to sit.
3. Submerge the tower container completely in the main tank to remove all air. This can be tricky if the tank is small, so plan your movements carefully.

Creating the Vacuum

Once the tower is submerged and filled with water, carefully lift it (mouth-down) onto its support stand. Ensure the opening is at least two inches below the main water surface to account for evaporation.

If you cannot submerge the whole container, place it on the stand full of air. Insert an airline tube into the tower, reaching the very top. Siphon the air out using a pump; as the air leaves, the water level will rise into the tower.

Managing Gas Exchange and Water Quality

One of the most common mistakes I see with an upside down fish tank is neglecting oxygen levels. Because the water in the tower is not in contact with the air, it can become stagnant if you aren’t careful.

Fish consume oxygen and release CO2. In a closed tower, the oxygen can deplete rapidly, leading to stressed or suffocating fish. To prevent this, you must ensure constant water circulation.

Ensuring Proper Flow

The easiest way to keep the water fresh is to aim a powerhead or filter outlet toward the opening of the tower. This forces oxygenated water from the main tank up into the elevated section.

Alternatively, you can run a small airline tube to the top of the tower to periodically suck out any trapped air and replace it with fresh water. Some advanced keepers even install a tiny submersible pump inside the tower itself.

Monitoring Algae Growth

Because the tower is often closer to light sources, algae growth can be more aggressive. Since you cannot easily reach inside with a standard scraper, consider using a magnetic glass cleaner designed for curved surfaces.

Best Inhabitants for Your New View

Not every fish is a good candidate for an upside down fish tank. You want species that are curious, active, and comfortable moving between different depths.

Goldfish are the classic choice for these setups. They are hardy, inquisitive, and look stunning when viewed through the magnified lens of a tower. However, they produce a lot of waste, so your filtration must be top-notch.

Small Tropical Fish and Shrimp

If you have a smaller setup, fancy guppies or neon tetras are excellent. They love to explore new areas and will frequently school inside the tower, creating a beautiful shimmering effect.

Cherry shrimp and Amano shrimp also love towers! They will climb up the supports and graze on any algae that forms on the tower walls. Watching a shrimp colony at eye level above the tank is truly a unique experience for any hobbyist.

Species to Avoid

Avoid labyrinth fish like Bettas or Gouramis. These fish need to breathe atmospheric air from the surface. If they get “trapped” at the top of the tower where there is no air pocket, they can actually drown. Always prioritize the biological needs of your species.

Maintenance Tips for a Crystal Clear View

Maintaining an upside down fish tank requires a slightly different routine than a standard aquarium. The most important task is monitoring the water line in your main tank.

If the water level in the main tank drops below the opening of the tower due to evaporation, the vacuum will break. This results in all the water in the tower rushing down at once, which can cause an overflow and a massive mess on your floor!

Routine Cleaning Steps

• Check the Seal: Every day, ensure no air bubbles are accumulating at the top of the tower.
• Top Off Water: Use an automatic top-off (ATO) system if possible to keep the main tank’s water level consistent.
• Clean the Acrylic: Use a soft cloth on the outside to prevent scratches. Acrylic is softer than glass and needs a gentle touch.

Dealing with Trapped Air

Over time, small bubbles from your filter or airstones may find their way into the tower. This “air pocket” will grow and eventually push the water level down. Simply use your airline tubing to suck the air out once a week during your regular maintenance.

Frequently Asked Questions (FAQ)

Can an upside down fish tank break my main aquarium?

It is possible if the main tank is not rated for the weight. Ensure your aquarium stand is sturdy and the base glass of your tank is thick enough. If you are using a large tower (over 5 gallons), consider placing the supports directly over the structural seams of the main tank.

Is it hard to clean the inside of the tower?

It can be. I recommend using a magnetic cleaner. If the algae becomes too thick, you will have to remove the tower, scrub it manually, and then go through the re-priming process to get the air out again.

Will my fish get stuck in the tower?

Generally, no. Most fish are very good at navigating. As long as there is proper flow and the opening is wide enough, they will swim in and out as they please. Just ensure there are no sharp edges on your support structure.

Do I need a special filter for this?

A standard hang-on-back (HOB) or canister filter works fine. The key is where you point the output. You want to move water into the tower to ensure it doesn’t become a “dead zone” for nutrients and waste.

Can I put plants in the tower?

Yes! Floating plants like duckweed or frogbit look amazing, but they can be hard to manage. Epiphytes like Anubias or Java Fern attached to the tower’s support structure are a better bet for a clean, professional look.

Conclusion

Building an upside down fish tank is a fantastic way to blend science with the art of aquascaping. It provides your fish with a unique environment and gives you a stunning focal point that is sure to start conversations.

Remember, the keys to success are structural stability, consistent water levels, and ensuring proper oxygenation. If you follow these steps, you will create a safe and beautiful home for your aquatic friends.

Don’t be afraid to experiment! Start small with a simple jar or small acrylic cylinder to get the hang of the vacuum process. Once you see your fish swimming high above the waterline for the first time, you will know the effort was absolutely worth it.

Happy fish keeping, and enjoy the view from the top!