At some point every aquarium hobbyist finds himself with an empty tank not being used. Part of the fun and excitement of the hobby is contemplating what to do with that tank next. One alternative to keeping more fish in the aquarium tank is to turn it into a terrarium instead.

A terrarium is a container that holds small plants or animals -- or both -- in closed and controlled conditions. They can range from custom-designed metal-and-glass cages to old plastic soda bottles, but nothing is as easy and practical for terrarium-making as your unused fish tank.

A fish tank turned into a terrarium needs a cover for the top of the tank so animals cannot escape. Metal covers with air holes are available in pet stores for this purpose.

The terrarium also needs a source of light and head. A basking lamp can supply both, and for extra heat, you can buy fake rocks that get warm when you plug them into an outlet.

Terrariums are fun for kids and grown-ups alike. A good idea is to keep a spare 5 or 10-gallon tank with a lid and light. When you find an interesting specimen like a newt or salamander, both of which I have kept in terrariums, you have an available habitat you can quickly ready to accommodate your new specimen.

• Terrariums.com
• Stormthecastle.com