Aquariums have a delicate aquatic life in balance. Choosing the wrong activated carbon can severely disrupt this balance and throw your aquarium into complete disarray. General Carbon has been supplying aquarium customers with the desired product, a coal based 4 mm pellet, our GC C-40 for many years. It is low in phosphates, designed for a low flow filter and good at removing colors. Typically, customers will put the carbon into pouches and place in the filter stream’s path so that circulating water will get filtered. The intention of the activated carbon is to remove colors and impurities. If you ever have an algae bloom with another supplier’s carbon, switch to ours. They are most likely using a coconut shell activated carbon which is high in phosphates. Ours will clean up your tank quickly. Please call with any questions.