Over time, sand will tend to scatter throughout the tank, so use your sand fountain periodically rather than on a day-to-day basis.
Sand fountains are some of the most interesting decorative items you can incorporate into the aquarium. Sand fountains create a constant trickle of sand that gives the impression of an underwater waterfall. Once you have constructed the air-powered apparatus, you can place other objects around it for camouflage.
Measure the distance between your tank's gravel bed and the surface of the water. Subtract about 2 inches from this total and cut a length of PVC equal to this figure with the hacksaw. For example, if the distance between the surface and your gravel is 10 inches, cut an 8-inch length of pipe. Connect a two-way connector to each end of the pipe, but do not adhere the pieces with silicone yet.
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Cut a 1-inch-long piece of PVC using the measuring tape and hacksaw. Insert this piece into one of the two-way couplers -- this end becomes the top side. Attach the three-way coupler to the other side of the 1-inch segment and rotate the coupler so that one open end points forward and the other points up.
Cut a 3-inch-long piece of PVC using the measuring tape and hacksaw. Place the pipe segment in the vise to hold it steady and use the drill and a quarter-inch bit to perforate the 3-inch-long piece. It does not matter exactly how many holes you create, but be careful not to compromise the integrity of the segment by drilling too many. Place the end cap over the open end of the segment and slide the segment into the two-way connector at the bottom of the fountain.
Connect the air pump to the air stone with the tubing. Thread the air stone through the open side of the three-way connector and down into the vertical pipe. Push the air stone until it rests at the bottom of the vertical pipe.
Place the fountain in your aquarium, using rocks, plants or decorative items to hold it in place and camouflage it. Create a basin near the intake tube with cage furniture or rocks -- this will provide a place for the sand to settle when it is ejected from the pipe.
Turn on the air pump. Bubbles should form inside the pipe and begin flowing up the fountain, ultimately emerging from the open side of the three-way connector. Slowly pour sand into the formed basin, near the perforated intake pipe. The action of the bubbles will create water current, which will carry the sand grains up the pipe. While the bubbles escape through the top opening of the fountain, the sand will continue traveling forward and slowly spill out of the outlet pipe.
Turn off the air stone, remove the fountain from the tank and disassemble it once you are sure that the fountain fits the tank and works properly. Allow the pieces to air dry. After it's completely dried, reassemble the device, using silicone at each of the pipe junctions.