Tap water contains chemicals and toxins that are harmful to fish if left untreated. API Tap Water Conditioner removes these toxins instantly, so you can add fish to your aquarium (or add them back after a water change) immediately. API Tap Water dechlorinates aquarium and tap water, detoxifies heavy metals, and may be used in both fresh and salt water. This super-concentrated formula treats up to 600 US gallons with just one ounce, making your aquarium a safe environment for your fish.