Activated charcoal is a highly adsorbent material that can remove impurities, organic substances, pollutants, and bad odors from water. It has a large surface area and a porous structure, which allows it to trap and hold various contaminants as water passes through it. By removing impurities, activated charcoal can help improve the water quality in the fish pond and create a healthier environment for the fish.
However, activated charcoal does not have any significant biological filtration capabilities and cannot remove ammonia or nitrites from the water. Therefore, it should be used in combination with other filtration media, such as bio-media, that provide biological filtration to maintain a balanced ecosystem in the fish pond.