API pH Down for Freshwater Aquariums API has been an industry leader in fish care, nutrition, treatments, testing and pond products for over 50 years, giving them a keen insight into your aquarium and its needs - making them the clear choice for fish enthusiasts around the world. API pH DOWN pH adjuster lowers the pH to make freshwater aquariums more acidic for fish and plants when levels rise too high. pH is the measure of acidic or alkaline conditions in water. Where a value of 7.0 corresponds to a neutral pH, pH values above 7.0 are considered alkaline, and pH values below 7.0 are considered acidic. Different fish need different pH levels to be healthy, so it is important to test your water regularly to ensure pH levels fall where they should. pH DOWN pH adjuster is fast-acting, colourless, easy to use, and will not cloud aquarium water. Because it is phosphate-free and nitrate-free, pH DOWN pH adjuster will not encourage algae growth. Water treatment to lower the pH (make the water more acidic) Use when the pH rises too high Suitable for freshwater aquariums Fast-acting, colourless, and will not cloud the water After something different? View all Fish Water Care Supplies. New to fish care? View our guide to Setting Up a Fishtank.