For something to be treated with a UV steriliser the water and the algae would need to come into direct contact with the ultra violet light. Blanketweed attaches itself to the walls, plant and rocks within your pond and is sometimes known to float on the water’s surface, this can prevent to blanketweed from being pulled through the filter and UV resulting in the algae not being treated.
In order to treat blanketweed you would need to purchase a specific treatment, this would bind to the blanketweed and break it down, this then allows the filter to pull the remaining algae through the UV system eradicating any spore the blanketweed may release, and finally filter it out.
You can find blanket weed treatments on our website by clicking here.
TIP: When treating for blanket weed it is recommended that you have a new UV bulb installed, this will ensure that the remaining algae spores come into contact with the ultra violet light.
For further information about blanketweed and how to keep it at bay in your pond, check out our blog article Blanketweed: Remedies and Control