How to Convert an Aquarium into a Paludarium

Evaluating the Aquarium

Converting a standard fish tank into a paludarium is an excellent way to enjoy both aquatic and terrestrial environments in one display. Before starting, evaluate your existing aquarium. Fill it with water and let it sit for 24 hours to confirm the silicone seams are sound, then drain it and wipe it clean with plain water or a diluted vinegar solution (avoid soaps and glass cleaners). Consider the height too. Taller tanks, such as a 20-gallon high (about 24 x 12 x 16 inches), provide sufficient vertical room for terrestrial plants to grow above the water line, while long, low tanks leave little growing space. Finally, remember that water weighs about 8.3 pounds per US gallon and wet soil and rock add even more, so make sure your stand is rated for the finished weight.

Can I Turn My Aquarium into a Terrarium?

Yes. A glass aquarium is one of the most popular starting points for a terrarium because it is strong, watertight, and widely available secondhand. A terrarium removes the standing-water zone (or keeps only a small water dish) and focuses on soil, plants, and humidity. If you do not want fish or a water feature, converting to a terrarium is simpler than building a paludarium. The main differences to plan for are:

• Drainage: An aquarium has no drain hole, so add a 1 to 2 inch drainage layer of LECA, hydro balls, or lava rock, then separate it from the soil with a mesh screen so the soil does not sink into the gaps.
• Substrate: Use a soil mix of coco coir, orchid bark, and sphagnum moss or a ready-made bioactive substrate about 3 to 4 inches deep. Avoid potting mixes with added fertilizer pellets, pesticides, or wetting agents.
• Ventilation: A solid glass lid traps humidity but can lead to mold and stale air. A screen top or partly open lid suits drier setups, while a mostly closed lid suits tropical builds.
• Lighting: Use full-spectrum LED lights, typically about 6500K, on a timer for 8 to 10 hours per day. Many planted-aquarium LEDs work well.

If you later want to add a stream, pond, or fish, you can convert the terrarium into a paludarium by adding a waterproof boundary and filtration. The comparison table below summarizes how aquariums, terrariums, and paludariums differ.

Can a Paludarium Have a Fish Tank?

Yes, and in practice most paludariums are built inside a fish tank. The water section of a paludarium works like a shallow aquarium, so it can house fish, shrimp, and snails. The key difference is that your water volume is much smaller than the tank's rated size, which affects stocking and water quality. Keep these points in mind:

• Choose small, peaceful species. Nano fish such as ember tetras, celestial pearl danios, Endler's livebearers, and white cloud mountain minnows suit shallow water. Avoid goldfish, cichlids, and other large, messy fish.
• Stock by actual water volume. Calculate your real water volume and stock conservatively, because small volumes build up ammonia quickly.
• Cycle the water first. Run the filter and cycle the water for about 4 to 6 weeks, until ammonia and nitrite read 0 ppm, before adding fish.
• Match temperatures. Pick fish that tolerate the same temperature range as your plants, and use a heater sized for your actual water volume (a common guideline is 3 to 5 watts per gallon).
• Secure the lid. Many fish jump, and a gap-free lid also keeps humidity high.
• Check compatibility. Fish may eat tadpoles or shrimplets, and some amphibians or crabs may prey on small fish. Research each species before combining them.

The species table below lists small fish and invertebrates commonly used in paludarium water zones.

How Do I Make My Own Paludarium?

Building a paludarium from an aquarium follows a clear sequence. Here is the overall process, with details for each stage below.

1. Plan your land-to-water ratio and sketch the layout.
2. Leak-test and clean the tank.
3. Build the land boundary and any background.
4. Install the filter, heater, and lighting.
5. Position hardscape such as driftwood and rocks.
6. Add the drainage layer, mesh screen, and substrates.
7. Fill the water zone slowly and start the cycle.
8. Plant the terrestrial, marginal, and aquatic zones.
9. Install the lid, set the lights on a timer, and monitor temperature and humidity.
10. Add livestock only after the water is cycled and the plants have settled in.

Designing the Land/Water Split

The first major design decision is the ratio of land to water. Consider what animals and plants you intend to keep. A setup for fish and shrimp may suit a balanced 50:50 or water-heavy layout, a habitat for terrestrial frogs may suit mostly land, and semi-aquatic turtles need far more water than a typical converted tank allows. Sketch out your layout, deciding whether the land will form a bank along the back, sit on one side, or act as a central island. The ratio table below lists common starting points.

Creating the Land Boundary

You must establish a structural boundary to hold the terrestrial substrate above the water. Popular methods include siliconing a glass or acrylic divider into the tank, building a false bottom framework using plastic egg crate, or sculpting a barrier using aquarium-safe expanding polyurethane foam and rocks. Use only 100% silicone labeled aquarium-safe (avoid bathroom or kitchen silicone, which often contains fungicides) and allow it to cure for at least 24 to 48 hours, longer for thick beads, until there is no vinegar smell. Whichever method you choose, it must be secure enough to prevent the land substrate from collapsing into the aquatic zone.

Filtration, Heating, and Circulation

Because a paludarium only partially fills the tank, standard Hang-on-Back filters often will not reach the water or will create excessive splashing. Internal submersible filters, small canister filters, or specialized paludarium filters are usually required. Ensure that the water circulates adequately to prevent stagnation and maintain healthy water parameters for aquatic life. A small pump can also drive a waterfall or stream feature. Use a submersible heater suited to your shallow water depth, and plug all equipment into a GFCI outlet with drip loops in the cords.

Recalculating Water Volume

Once you have planned the land and water zones, you must account for the drastically reduced water capacity. The physical space taken up by the land foundation and the lower overall water depth mean your 20-gallon tank will no longer hold 20 gallons of water. For example, a 20-gallon high tank (24 x 12 inches) with half the footprint as water at a depth of 6 inches holds about 3.7 gallons (864 cubic inches divided by 231). It is important to calculate the new water volume so that you can correctly dose water conditioners and appropriately size your heater and filter. The table below shows estimates for common US tank sizes.

Substrate and Plants

With the hardscape and boundary in place, you can add your terrestrial and aquatic substrates. Use a high-quality bioactive substrate for the land portion to support healthy plant growth and microfauna, and fine gravel, sand, or aquarium soil in the water zone. Finally, select appropriate paludarium plants, placing moisture-loving marginal plants near the water's edge and true terrestrial plants higher up on the land structure. Popular choices include java fern, anubias, pothos, peace lily, ferns, mosses, bromeliads, fittonia, and creeping fig.

Temperature, Humidity, and Lighting

Most tropical paludariums run at about 72 to 82 degrees Fahrenheit with 60 to 90 percent humidity on the land side. Use full-spectrum LED lighting on a timer for 8 to 10 hours per day, and monitor conditions with a digital thermometer and hygrometer rather than guessing.

Are Paludariums Hard to Maintain?

Paludariums are moderately difficult. They are more demanding than a basic fish tank or terrarium because you are managing two systems at once: a water system (filtration, water changes, the nitrogen cycle) and a humid land system (misting, pruning, mold control). The good news is that a well-planned, established paludarium can be fairly stable, and many hobbyists spend roughly 30 to 60 minutes per week on routine care. New setups need more attention for the first few months while plants root and the water cycle matures.

• What is easy: Hardy plants grow quickly in the humid air, the water zone buffers temperature swings, and a bioactive cleanup crew of springtails and isopods helps control mold and waste.
• What takes effort: Balancing humidity against ventilation, keeping the land boundary sealed, controlling algae, and keeping water parameters stable in a small volume.
• What reduces work: Choose hardy plants, avoid overstocking, use a timer for lights, and keep a simple maintenance routine.

The schedule and troubleshooting tables below outline typical tasks and fixes.