At times it is necessary to add tap water to the aquarium as part of a water change or a top up. Tap water is designed for human use and therefore contains high levels of chlorine to kill germs. In addition it may contain varying levels of toxic heavy metals. Both chlorine and heavy metals are toxic to fish and will cause them long term damage and stress. Leaving water to stand will not remove all of these factors and so is not an alternative to using a water conditioner. Aqua Safe works by instantly neutralising these harmful substances and should be used every time new water is added to the aquarium. In addition Aqua Safe also reduces stress promotes wound healing and protects against infection and adds a protective coating to the fish.