HyperZeo's effectiveness varies depending upon on the amount of nitrogenous compounds initially present in the aquarium and the rate at which the substances are processed by the biological filter.That rate,in turn, depends upon the population density and on the efficiency of the filter system. Use regular water testing to determine the optimum replacement schedule for the product. HyperZeo is suitable for all aquariums. It does not alter pH and is safe for all aquarium inhabitants.