Hozelock Cyprio Blanketweed Treatment 250g - 3959 The Blanketweed Pond Treatment by Hozelock is an effective pond treatment for green blanketweed and is harmless to fish. Blanketweed, the scourge of many pondkeepers, can layer on the top of your pond. This is a fast working treatment that eliminates Blanketweed and is harmless to fish. The crystals are scattered evenly over the blanket weed (avoid scattering directly onto other aquatic plants). Can be used at lower dosage to prevent build-up of blanketweed. The Blanket Weed Pond Treatment is a fast working biological treatment to eradicate green water blanket weed. It is harmless to fish and pond life and can treat up to 8,000 litres of water. Fast working, effectively treat blanket weed with this treatment.