Can A Terrarium Be Used As An Aquarium – Your Complete Safety

Written ByHoward Parker

Have you ever stumbled upon a beautiful, uniquely shaped glass terrarium at a thrift store or a garage sale and thought, “That would make an amazing little fish tank”? It’s a common thought for any creative aquarist looking for their next project.

You agree that repurposing something old into a stunning new aquatic home is a fantastic idea. But a nagging question probably stopped you: is it actually safe? Can a container built for soil and plants truly handle the constant pressure of water?

I promise this guide will give you the confidence to answer that question. As a seasoned aquarist, I’ve seen both the triumphs and the disasters of DIY tank projects. I’m here to walk you through everything you need to know, from the critical safety checks to the step-by-step conversion process.

We’ll cover the fundamental differences between the two enclosures, how to inspect your specific terrarium for aquarium-worthiness, and the exact steps to transform it into a safe and thriving home for your fish. Let’s dive in and see if we can turn that glass box into an aquatic masterpiece!

Terrarium vs. Aquarium: Understanding the Critical Differences

Before we even think about adding water, it’s crucial to understand why a terrarium and an aquarium aren’t built the same. It’s like comparing a garden shed to a submarine—they might look like boxes, but they’re engineered for completely different environments.

Glass Thickness and Water Pressure

The number one difference is the glass itself. Aquariums are designed to withstand constant, immense pressure from the water within. This is called hydrostatic pressure, and it pushes outwards on every single panel, 24/7.

Because of this, aquarium glass is significantly thicker and often tempered for strength. A terrarium, on the other hand, is only meant to hold lightweight soil, plants, and a bit of moisture. Its glass is usually much thinner and not rated for the relentless pressure of a full water column. Using a thin-walled terrarium is a major risk.

Sealant and Silicone Safety

The glue that holds the glass panels together is another critical point. Aquariums are sealed with 100% silicone that is specifically formulated to be waterproof and, most importantly, non-toxic to aquatic life once cured.

Terrariums often use different adhesives or silicones that may contain anti-fungal or anti-mildew chemicals. These additives are great for a humid, soil-based environment but can be lethally toxic to fish, shrimp, and snails. Never assume the sealant in a terrarium is safe for an aquarium.

Shape, Structure, and Support

Many aquariums, especially larger ones, feature a plastic or metal frame along the top and bottom. This isn’t just for looks; it provides crucial structural support and a level surface for the glass to rest on. Most terrariums are frameless, relying solely on the silicone seams for integrity—seams that, as we just learned, might not be up to the task.

The Essential Safety Checklist: Can Your Terrarium Be Used as an Aquarium?

So, you have a terrarium in hand and you’re ready to assess it. This is the most important part of our can a terrarium be used as an aquarium guide. Follow these steps carefully. Your success—and the safety of your home from leaks—depends on it.

  1. Inspect the Glass for Flaws: Place the terrarium in a well-lit area. Run your fingers along every edge and surface. You are looking for any chips, cracks, or deep scratches. A tiny chip that’s harmless with soil can become a catastrophic failure point under the constant stress of water pressure.

  2. Evaluate the Silicone Seals: Look closely at the inside seams. Is the silicone peeling, dry, brittle, or pulling away from the glass? Does it look like a clear or black bead, or is it a different color? If the sealant is anything but 100% silicone (which is what you’d find in a standard aquarium), you must assume it’s unsafe and will need to be replaced.

  3. Consider the Size: Be realistic. This project is best suited for small terrariums (under 10 gallons, and ideally under 5). The larger the volume, the greater the pressure and the higher the risk. A large reptile enclosure is almost never a good candidate.

  4. The All-Important Leak Test: If the glass is flawless and you’re committed to resealing it, it’s time for a test. Take the terrarium to a safe place where a leak won’t cause damage, like a garage, basement floor with a drain, or inside a bathtub.

    • Fill it about one-third of the way with water.
    • Mark the water line with a dry-erase marker.
    • Leave it for 24 hours. Check for any drop in the water level (below your mark) and for any dampness around the base.
    • If it holds, fill it two-thirds of the way and repeat for another 24 hours.
    • Finally, fill it completely and test for a final 48 hours.

If your terrarium passes this rigorous test, you can proceed with cautious optimism! If it fails at any stage, it is not safe to use as an aquarium.

How to Convert Your Terrarium: A Step-by-Step Guide

You’ve done your safety checks and you’re ready to go! This section covers how to can a terrarium be used as an aquarium successfully. For 99% of terrariums, this process will involve a full reseal.

Step 1: Resealing Your Terrarium (The Most Important Step)

Do not skip this step. Even if it passed the leak test, the original sealant is likely not fish-safe. This is one of the most important can a terrarium be used as an aquarium best practices.

  1. Gather Your Supplies: You will need a tube of 100% aquarium-safe silicone, a caulking gun, a razor blade scraper, acetone (or rubbing alcohol), paper towels, and painter’s tape.

  2. Remove the Old Sealant: Carefully use the razor blade to cut away and scrape all the old silicone from the inside seams. Be thorough! Any old sealant left behind will prevent the new silicone from making a perfect bond.

  3. Clean and Prep: Once all the old silicone is gone, clean the seams and surrounding glass with acetone on a paper towel. This removes any residue and oils, ensuring a strong, waterproof seal. Let it dry completely.

  4. Tape the Seams: For a clean, professional look, apply painter’s tape on the glass on either side of each seam, leaving a small, uniform gap where the new silicone will go.

  5. Apply New Silicone: Apply a steady, continuous bead of new aquarium-safe silicone into each seam. Work quickly but carefully to ensure there are no gaps or air bubbles.

  6. Smooth the Bead: Immediately after applying, wet your finger and run it along the bead to smooth it into a concave shape. This ensures it makes full contact with both panes of glass.

  7. Cure Completely: Remove the painter’s tape and let the silicone cure. This is non-negotiable. It must sit in a well-ventilated area for at least 48-72 hours. It will have a strong vinegar smell while curing; when the smell is gone, it’s fully cured and safe.

Step 2: Choosing the Right Equipment

Because your new tank lacks the standard rim of a manufactured aquarium, you’ll need to be creative with equipment.

  • Filtration: A hang-on-back filter is likely not an option. Instead, opt for a gentle sponge filter (perfect for shrimp and betta fish) or a small internal power filter.
  • Heating: A small, fully-submersible preset heater is your best bet. Look for models designed for nano tanks and bowls.
  • Lid & Lighting: Terrarium lids are designed to hold in humidity, not support lights or stop fish from jumping. You will likely need to create a custom lid from acrylic, polycarbonate, or even a simple craft mesh. For lighting, a small clip-on LED light is a perfect solution.

Best Inhabitants for Your Converted Tank: Small and Mighty Choices

Now for the fun part! The benefits of can a terrarium be used as an aquarium really shine when you create a unique nano environment. Given the smaller size and DIY nature, it’s best to stick with small, low-maintenance inhabitants.

Nano Fish Favorites

If your converted tank is at least 5 gallons, you have some great options. A single Betta fish would view this as a palace! A small school of Celestial Pearl Danios or Chili Rasboras would also create a stunning, active display. Don’t worry—these fish are perfect for beginners!

The Invertebrate Option: A Shrimp Paradise

For a truly sustainable can a terrarium be used as an aquarium project, consider a shrimp-only tank. A colony of Neocaridina shrimp (like the popular Red Cherry Shrimp) is fascinating to watch, easy to care for, and has a very low impact on the water quality. They are an amazing, eco-friendly choice.

Common Problems with Can a Terrarium Be Used as an Aquarium (And How to Solve Them)

Even with the best preparation, you might encounter a few hiccups. Here are some of the most common problems and how to head them off. This is a critical part of any good can a terrarium be used as an aquarium care guide.

Problem: The Seals Fail (The Nightmare Scenario)

Solution: This is almost always due to improper cleaning before resealing or not letting the silicone cure long enough. The only solution is to drain the tank immediately, dry it completely, and restart the resealing process from scratch. This is why the initial leak test and patient curing are so vital.

Problem: Glass Distortion and Viewing Issues

Solution: Some terrariums use thinner or curved glass that can slightly distort the view of your fish. Unfortunately, there’s no fix for this. It’s simply a characteristic of the container. Embrace its unique look and be aware of it when you’re aquascaping.

Problem: Finding Equipment That Fits

Solution: This requires planning. Before you even start the conversion, measure your terrarium and research equipment. Look for “nano” or “pico” aquarium gear. Sponge filters, small internal filters, and clip-on lights are your best friends in a DIY build like this.

Frequently Asked Questions About Using a Terrarium as an Aquarium

What kind of silicone should I use to reseal a terrarium?

You must use 100% silicone sealant that is explicitly labeled as “aquarium safe.” A great option is GE Silicone 1 All-Purpose. Critically, ensure the label says it does not contain any mold or mildew inhibitors, as these are toxic to fish.

Can I use a large reptile terrarium with sliding doors?

It’s highly discouraged. Those sliding doors are impossible to seal reliably and represent a massive weak point. The frames are also not typically designed to handle the outward pressure of water. Stick to smaller, 5-sided glass boxes for this project.

Is it cheaper to convert a terrarium than buy a new aquarium?

Not always. By the time you purchase the terrarium (if you don’t have one), aquarium-safe silicone, a scraper, and a custom lid, you may have spent as much as a standard 5 or 10-gallon aquarium kit from a pet store. The real benefit is in creating a unique, custom-sized tank that you can be proud of.

How do I calculate the volume of my terrarium in gallons?

Easy! Use this simple formula: Measure the Length, Width, and Height in inches. Then, calculate: (Length x Width x Height) / 231 = Volume in U.S. Gallons. Knowing your true volume is essential for choosing the right number of fish and the correct heater size.

Your Unique Aquatic World Awaits

So, can a terrarium be used as an aquarium? The answer is a resounding yes, with careful work. It’s not a simple plug-and-play project, but one that requires diligence, patience, and a healthy respect for the power of water.

By following this guide—from the initial safety inspection to the crucial resealing process—you can confidently transform a simple glass box into a beautiful and safe aquatic habitat. You’re not just saving a piece of glass from the landfill; you’re creating a one-of-a-kind world for your aquatic pets.

Take your time, trust the process, and get ready to enjoy a stunning nano aquarium that is truly your own. Go forth and create!

Howard Parker
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