The nitrate flud should not be dosed directly in to an aquarium.

The nitrate fluid is completely safe within the rates that are used for the reactors. If a little to much is dosed in to a reactor and it is not consumed by the bacteria, causing some to escape, it will feed natural bacteria in the system itself. In cases of severe overdosing you will see the water in the tank go cloudy, as there is bacterial bloom. Bacteria blooms can reduce oxygen and irritate fishes mucus membranes so should be avoided.