Barley straw is organic and harmless to pets and wildlife. The sturdy mesh bag contains a generous 300g of barley straw bale - make sure to check weights and sizes when comparing similar products. When it rots it will produce a trace amount of hydrogen peroxide, which will not harm fish or aquatic plants but will stop algae like blanketweed developing properly. The bag also contains harmless bacterial spores packaged inside PVA, which will dissolve in water - the spores are safe for humans, plants and wildlife and will rapidly multiply in the pond to help clean water of black sludge and pollutants, improving water clarity and reducing foul odours and ammonia.