I use a pelletized coal based activated carbon in a paint strainer in an Aquaclear 70. It has very little dust, and does not clog like granular would. Here is a little information that I gathered:
It has the medium and large sized pores that are needed for aquarium use for removing odor, color, and chemicals, and it is low in soluble ash, while lignite based activated carbon is high in soluble ash. It is also much harder than lignite based activated carbon, so will hold together better than lignite based activated carbon.
Coal based activated carbon originates from coal that has undergone steam activation process to create its activated carbon form. During activation, it creates millions of pores at the surface of the carbon thus increasing the total surface area. Activated carbon pores can be divided into three general sizes Micro-pores (diameter in the range of less than 2 nm), Meso-pores (diameter in the range of 2 -- 25 nm), and Macro-pores (diameter in the range of above 25 nm). Coal based carbon has mainly meso-pores and macro-pores and due to its unique distribution of pores diameter, coal based activated carbon are very popular in the gas phase purification, potable water purification industries, waste water purification industries and aquarium/pond water purification industries.
David