As soon as Pure Aquarium is placed into an aquarium with fish, and dechlorinated water of the correct temperature, something will happen. Bacteria will leave the ball in their millions and seed the aquarium. You can’t see them but they are there and working, and Pure’s bacteria has been independently tested and counted. The least visible difference will be on a mature, healthy, well filtered aquarium with already crystal clear water, but even then solid waste levels may be lessened in the tank and inside the filter. The most difference and benefit will be seen in dirty, poorly filtered tanks, with water clarity and quality issues.