Waterlife Algizin P is a highly acclaimed algicide which kills blanket weed FAST - results can usually be seen within 1 week ! Waterlife\'s popular Algizin P product is a true algicide (as opposed to an inhibitor) and as such it is registered with the HSE. It is blanketweed specific and will not harm oxygenating plants lillies marginals or other aquatic plants. It is also safe with fish and filtration. Repeat use during the growing season every 4 to 6 weeks or when re-growth occurs. 125ml - treats 9000 litres.