If you want a natural way to prevent algae growth in your water reservoir, the AQUAPRO Bionatural Feature Frog Block is made for you. The Bionatural Frog Block has been made with natural bacteria strains designed to control and starve algae of the necessary nutrients needed to grow. Being a bionatural product, it is harmless to fish, pets, pond plants and wildlife, allowing for complete peace of mind whilst dosing your pond. When used as directed with a pump or filter system, the block has further abilities to prevent mosquito larvae from developing, whilst still being safe for any animals that consume the water. Suitable for ponds up to 1000 litres in size, not recommended to be used in smaller water features. Once the block has dissolved, the preventative effect can last up to 3 months within the water body.