Key Features Stops algae growth and prevents ammonia problems Can be used in all types of pond filters Increases efficiency of filters Plastic, durable and washable High surface area to allow for more bacteria to colonise The Superfish Bio Blocks are a plastic filter media featuring a large surface area for the growth of vital bacteria for water filtration. This filter media is specifically designed to stop algae growth and prevent ammonia problems in your pond. This filter media is ready out of the bag to go straight into your filter and is easy to remove and maintain. Specifications Bag Size: 10 Litres