Tetra Pond Aqua Safe 500ml makes tap water suitable for fish by removing harmful compounds and adding beneficial substances. 500ml of Tetra Pond Aquasafe treats 10000 litres / 2200 gallons At times it is necessary to add tap water to the pond, following maintenance or evaporation. 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. Tetra Pond AquaSafe neutralises harmful elements in tap water, and adds beenficial substances to create healthy, fish-friendly water