DIY Old Fish Tank Terrarium: How To Make Aquarium Terrariums

By: , Credentialed Garden Writer
tropical terrarium
Image by alekseystemmer

Converting a fish tank into a terrarium is easy and even younger kids can make aquarium terrariums, with a little help from you. If you don’t have an unused aquarium in your garage or basement, you can pick one up at your local thrift shop.

Fish Tank Terrarium Ideas

Here are some ideas for converting a fish tank into an aquarium:

Creating Aquarium Terrariums

Here are simple steps for making a miniature, self-contained ecosystem. The finished product is beautiful, and once established, caring for a DIY fish tank terrarium requires very little effort. 

  • Closed aquarium terrariums are easiest and are well-suited for plants that like humidity. Terrariums with open tops dry out quickly and are best for cacti or succulents.  
  • Scrub your aquarium with soapy water and rinse well to remove all soap residue.
  • Start by putting one to two inches (2.5-5 cm.) of gravel or pebbles in the bottom of the tank. This will allow for healthy drainage so the roots don’t rot.
  • Add a thin layer of activated charcoal. Although charcoal isn’t absolutely necessary, it’s more important with an enclosed terrarium because it will help keep the air in the aquarium clean and fresh. You can also mix the charcoal with the gravel.
  • Next, cover the gravel and charcoal with one to two inches (2.5-5 cm.) of sphagnum moss. This layer isn’t a must, but it will prevent potting soil from sinking into the pebbles and charcoal.
  • Add a layer of potting soil. The layer should be at least four inches (10 cm.), depending on the size of the tank and your fish tank terrarium design. The terrain in your tank needn’t be flat, so feel free to create hills and valleys – much like you’d see in nature.
  • Depending on your fish tank aquarium design, you can embellish the tank with twigs, rocks, shells, figurines, driftwood, or other decorative objects.

Caring for Your Aquarium Terrarium

Don’t put the aquarium terrarium in direct sunlight. The glass will magnify the light and bake your plants. Water only if the soil is almost completely dry.

If your aquarium terrarium is closed, it’s essential to vent the tank occasionally. If you see humidity on the inside of the tank, take the lid off. Remove dead or yellowing leaves. Prune plants as needed to keep them small.

Don’t worry about fertilizer; you want to maintain fairly slow growth. If you think the plants need to be fed, use a very weak solution of water-soluble fertilizer occasionally during spring and summer.

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