Make a cave in an aquarium for pet fish and other aquatic life that enjoy privacy or are territorial. Homemade caves can also add to the realistic look of a fish tank. Only basic materials and an hour or two are needed to create an aquarium cave your fish will love.
Select a small plastic flower pot or a plastic bowl the correct size to build a cave in you aquarium. This will depend on the size of the fish tank and the length of the fish who would like to use the underwater cave.
Cut the pot or bowl in half so it forms a half circle or slightly taller shape. You can leave the entire pot or bowl intact if your aquarium gravel or substrate is deep enough to bury it in. This will help the aquarium cave stay in place better.
Squeeze aquarium-grade silicone sealant onto the outer sides of the pot or bowl and stick on small rocks, pebbles or aquarium gravel. Do this in smaller sections so the sealant does not dry before you get the rocks on. Allow the pot to dry completely before inserting it into the fish tank.
Build a larger or different type of cave by using larger rocks stuck together securely with aquarium-grade silicone sealant. Start with larger rocks on the bottom and stick a flat rock or multiple smaller rocks at the top. You will need a large amount of silicone to make sure this fish tank cave is secure.
Position the aquarium cave you made in the fish tank where fish will be able to use it. If desired, put a live plant such as Java moss on the cave and wrap a piece of monofilament line to hold it on until roots form. This will give the cave a more realistic look in the pet fish habitat.
Clean all rocks and pots with clear water before use.