R U treating tap water for a tank?
If so I wouldnt add either adn go with a good RO/Di unti and it will take care of all that without adding a chemical to the tank.
also if you decide to add a chemical then it can cause a skimmer to go nuts so make sure to watch that.
Mike
What are you using it for? Amquel works well, but keep in mind that they are both just a temporary fix for whatever the situation is. It is best to address the source of the problem.