Hagen

Yes, all Nutrafin remedies and treatment products are safe for use while fish are in the aquarium. The Biological Clarifier - B-Clear - is a combination of a powerful team of bacteria that gradually breaks down accumulated wastes in the tank. It is an ongoing process and there is no danger to fish with the regular use of the product over time.
As the bacterial populations supplemented by the regular use of B-Clear build up, they tend top prevent other, less desirable bacteria or other pathogens from gaining a foothold in the aquarium as well, making the environment that the fish live cleaner and less prone to other problems. Its use is always recommended with fish in the aquarium.