Every good fisher keeper from time to time will need to add tap water to their aquarium usually when carrying out fish tank cleaning and maintenance. Whilst tap water is completely safe for humans the levels of chlorine and varying levels of heavy metals in tap water are harmful to fish. A perfect way to neutralising these harmful substances is to use a water conditioner. Tetra’s Aquasafe instantly effectively removes the harmful tap water products, reduces stress, supports the fish's protective mucus layer and adds iodine, magnesium, and vitamin B for health and vitality in fish. Tetra Application Guidance: Add 5ml per 10 litres of tap water.