Sand filters, also called fluid bed filters, promote biological filtration in the aquarium. They work by suspending sand with water pressure, allowing beneficial bacteria to colonize the sand. These bacteria break down fish wastes into less toxic compounds. Build your own sand filter from parts available at pet shops and hardware stores.
When building your own sand filter, many of the specifics depend on the equipment you choose. For example, you will need a submersible water pump rated for at least six times your aquarium volume per hour. Once you pick this, you will need to select vinyl tubing that can fit the pump, and bulkhead fittings that can fit the tubing. Lastly, you will need a clear, watertight, all-plastic water bottle with a large enough lid to accommodate both bulkhead fittings and still screw shut. Teflon plumber's tape also helps with waterproofing. Most of these supplies can be obtained at pet shops and hardware stores, though you will need to find your bulkhead fittings online.
Plumbing the Filter
First, drill two holes into the lid of a sports bottle large enough to accommodate the bulkhead fittings. Install the bulkhead fittings by twisting them in place. make sure the rubber or silicone flange is on the inside of the bottle. Next, cut enough vinyl tubing for an "in" line and an "out" line. The in line must reach all the way from the submersible pump inside the aquarium to your filter, and the out line must reach from the pump back to the aquarium. Next, cut a length of tubing that reaches from the inner side of the bulkhead fitting to a spot just above the bottom of the sports bottle. Most aquarium pumps and vinyl tubing slide on without requiring plumbing.
First you must rinse the sand. To do this, place it in a bowl or bucket and add enough water to cover the sand. Stir it up, releasing dust, and then pour off the water. Repeat until the water comes off clear. The exact amount of sand you will need varies with the size of container you picked, but use enough to fill the container about one-quarter with sand. More than this and the sand can blow out through the out line.
Final Assembly and Leak Testing
You must test the filter before letting it run unsupervised on an aquarium. First, fit the in-line to the submersible pump. Then, fill the water bottle and tubing with water. This "primes" the pump -- many water pumps cannot start unless all of the plumbing is filled with water. Then, turn on the pump. If everything works, you will see the water from the pump push the sand upwards, but not all the way to the out-line bulkhead fitting. Run the filter for at least 48 hours before putting it into service to make sure none of the hoses slip off or leak. Ideally, test the whole thing in a bathtub with a bucket as the "aquarium."
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