Introduction OF® ACTIVA BLOCK is a super-charged activated carbon block designed to maximize absorption of aquarium water coloration, odours, toxic pollutants ( e.g. insecticides and chemicals ) and medication. Ideal for all types of aquarium. Highly porous natural Bamboo Activated Carbon and Sepiolite Clay minerals are precision-cut into a Cuboidal Matrix Design featuring 1400 micro-tunnels; this greatly increases its surface area and boosts its ability to draw out toxic pollutants from your aquarium water quickly and efficiently. As a result, this little 500g cube packs the equivalent absorptive capacity of 20kg worth of regular activated charcoal powder, or 40 times its body weight in absorptive power! More Effective. Less Mess. Comparison of the precipitation caused by regular activated carbon granules versus the clean and clear water of OF® ACTIVA BLOCK. Rapid Absorption! The Cuboidal Matrix Design featuring 1400 micro-tunnels greatly increasing the capability to absorb toxic pollutants! Absorption Test Results OF® ACTIVA BLOCK absorbance efficiency graph based on 250g block and 1mg Methylene Blue. Test method : US EPA Methylene Blue method