Call us on 01246 240880

What is Blanket Weed?

Blanket weed is a type of algae, scientifically called filamentous algae. It’s also commonly known as string algae or silk weed. Pond owners often struggle to identify blanket weed because it occurs in different forms.

Typically, it appears either floating on top of or submerged within pond water as clumps of thick green, hair-like strands. These dense clumps have no leaves, stems or roots but will attach themselves to pond walls.

Ornamental ponds with high sunlight exposure and organic nutrients create the perfect environment for it to thrive.

Not sure if you have blanket weed?

Watch this video:

5 Pond Problems Caused by Blanket Weed


  • 1. Aesthetics. Blanket weed ruins the appearance of a pond.


  • 2. Not only does it make ponds unappealing, it’s often a sign of chemical imbalance in the pond. (Yes, even if the water looks clear!)


  • 3. It consumes large amounts of oxygen from pond water. This creates a harmful environment because aquatic plants and fish are forced to compete with it for oxygen. Especially in summer, when pond oxygen levels are low.


  • 4. Floating blanket weed deprives submerged oxygenating pond plants of sunlight. Preventing their process of photosynthesis and further reducing pond oxygen levels.


  • 5. Fish can get tangled in submerged string algae. When unable to escape, fish can potentially suffocate and die.

What causes blanket weed?

It has two main causes, excessive sunlight and nutrients. Nutrients in pond water, caused by the build-up of organic matter, act as a food source. While sunlight stimulates growth through the process of photosynthesis. These two factors also the reason it is often a recurring problem.

How to Remove It

Pond owners often attempt to remove string algae with a pond net skimmer. However, this method alone is not advisable. Moving/pulling it while it’s alive releases spores into the pond water, that will cause more to grow in the future. To remove it from your pond, you will first need to kill it.

For removing floating type, we recommend you use Blanketweed Klear. This is a granular treatment that you can apply directly on top of the blanket weed and works within 24 hours to kill it, meaning you can safely remove it after a day.

To remove the submerged type, we suggest you use Algae Klear Xtra. A liquid treat, which effectively travels deep into the pond, to where the submerged string algae has anchored itself to. After killing it and cutting it off from its environment, Algae Klear Xtra allows you to safely remove it from the pond.

  • Blanketweed Klear

    Fast acting blanket weed killer that targets blanket weed floating on the surface of the pond and kills it within 24 hours. The unique bacteria then help to prevent any blanket weed from re-growing in the pond.

  • Algae Klear Xtra

    Fast acting pond algae treatment that targets and kills submerged blanket weed and string algae within 2 weeks. Works at any temperature and prevents the re-growth of algae due to it’s unique UV light filter.


How to Prevent It

Simple tips to help you prevent blanket weed from returning in the future:

  • Fill your pond with aquatic plants that will absorb excess nutrients in the pond.
  • Keep an appropriate stock of fish to suit the size of your pond.
  • If and where possible, provide your pond with shade.
  • Check your water quality regularly with a test kit to make sure your pH, KH and GH levels are balanced.

Related posts

4th February

Pond Care: Common Questions Answered

Find out more
3rd May

Pond UV Lights: A Beginner’s Guide

Find out more
8th September

Featured Product: Pond Klear

Find out more
Share this page


Envii Payment Methods
Envii Offer Sign Up