ChemiCarb is a carbon that can be used in your filter to help to remove toxins and improve water clarity. The loose tub means that you can use as much or as little as you need, and it can be used with all types of filter, of any brand, as you just fill the included media bag to suit the shape and size of the filter chamber you have. This means you can just take out and fill the bag, close it up, and install in your filter, and replace as needed.
This ChemiCarb is a form of chemical filtration, and contains no phosphates and is suitable for freshwater use. It works in the tank by removing any dissolved organic waste from your aquarium, as well as dyes, meaning you have crystal clear water.