Items you will need
Clay shaper tools
Lead-free paint glaze
To create a natural-looking environment in an aquarium, use plants and decorations that closely resemble the natural habitat of the fish housed in the tank. Pet stores sell rocks and caves the fish use to hide in, lay eggs in and live in, but they are expensive. Making rocks and caves for aquariums can be accomplished with clays, allowing the aquarium owner to make any size and shape desired.
Wet the clay and wedge it to remove air pockets. Wedging is important, because if bubbles remain in the clay, it may explode when it is fired later. To wedge, lift the clay and slam back down onto a table or other flat surface for 10 minutes.
Make the rocks. For each one, pull off a piece of clay and shape it into an oblong, tall and sharp or rounded rock.
Make the caves. Unlike the rocks, the freestanding caves will be hollowed out. For each cave, take a piece of the clay and flatten it to a thickness of about ½-inch. Then mold into a shape with a flat bottom and a rounded top. Fish will use the cave to hide in, so it needs at least once entrance. Since the clay is still soft, use a pottery toolkit containing a wooden knife or trimming tools to make a hole in the clay for the entrance.
Etch and mark the outsides of the caves and rocks, using clay shaper tools available from pottery- or art-supply stores. Make creases and crevices to resemble real rock.
Allow the pieces to air dry overnight. The following day, the clay will still be soft enough to add more markings or entrances to finish the pieces, if needed.
Fire the clay in a kiln. Kilns are available for home purchase but are several hundred dollars. Inquire at local art-supply stores about places that provide access to kilns for a fee.
Use lead-free ceramic paint to paint the pieces. To make natural-looking rocks and caves, paint on mosses and shadows.
If you don’t want to make your own caves, use clay flowerpots. For each one, turn a pot on its side, bury the pot partly into the gravel or sand and add pieces of slate and stone to make a rock façade in front of the pot.
You can also make a cave out of pebbles. Boil the pebbles to get rid of any chemicals and use aquarium-safe silicone to glue the rocks together to form a cave.
Not all rocks are safe for aquariums. Do not use lava or marble because the lava is sharp and can harm fish, and marble releases chemicals that harden the water, making it uninhabitable by most fish.
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