Aquarium charcoal, also called activated carbon, provides a means of chemical filtration for fish tanks. The material consists of charcoal granules that have been heat- and chemically treated to make them more porous, increasing the surface area available for bonding with foreign matter. You'll have to periodically replace aquarium charcoal, and you'll need a means of binding it. A simple mesh aquarium charcoal bag you make at home will do the trick.
Assemble Your Materials
Take some care in assembling your materials. First, you need a sewing machine. You could stitch a mesh bag by hand; but since you won't see the bag tucked away in a filter and the charcoal is ultimately disposable, it is probably not worth the time of sewing one by hand. For mesh, you need a material that will not leach dangerous chemicals into the aquarium water. Many pet shops sell aquarium filter floss for DIY filters, but any kind of undyed nylon mesh should work. You can also use mosquito netting as long as it is not treated with pesticide. Along similar lines, you should stick to uncolored nylon thread. Avoid cotton mesh or thread, since it can slowly rot in aquariums.
Putting It All Together
Aquarium charcoal has many applications. The exact size will depend on how you plan on using your carbon. Use it sparingly; as little as 3 tablespoons of carbon can remove discoloration from a 50-gallon aquarium. Cut two identical-size sheets of mesh. Use sewing pins to hold the mesh together while you sew. Sew three sides together with topstitching, a sewing machine stitch that can hold mesh together. This will form a pocket. Place your activated carbon in the pouch and sew the last side together, locking the carbon inside. Rinse your bag to remove any carbon dust, then add it to your aquarium. You can hide charcoal bags in power filters, canisters filters and sumps. Replace aquarium charcoal every few weeks.
You can use the same mesh bag with other materials for different effects. For example, you can use zeolite instead of carbon. Zeolite absorbs organic waste and can be recharged with saltwater several times before it must be discarded. You can also use peat, which softens and acidifies water. Fish from rain forest rivers and peat bogs thrive in such conditions. Conversely, you could fill your pouch with crushed limestone or other calcium-rich materials. These have the opposite effect, raising the pH and hardness of water. Some fish thrive in such conditions, like livebearers and African cichlids.
If you don't have a sewing machine or time to hand-stitch the bags, many pet shops sell small mesh bags that can hold carbon or other water treatment materials. In a pinch, you also use a clean nylon stocking to hold aquarium carbon. Just dump it into the toe, tie a knot in the hose and cut off the excess. Many types of aquarium filters have their own replaceable carbon inserts; they might cost more than homemade mesh bags, but they're undoubtedly convenient, if not as convenient as a a DIY bag you've made yourself.
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