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.