S.T. International Activated Carbon and Bacteria Housing for Low-Water Level Filter Filled with Powerful Activated-Carbon and Bio-Sponge These ready-to-use disposable cartridges remove waste particles, odors and discoloration and are easily changed A Powerful Activated Carbon located in the first stage designed to remove color, odor and harmful toxic substances in the water A Bio-Filter Sponge (serving as the second stage) cultivates filtering bacteria which eliminates ammonia and builds up the cycling ecosystem