Blanket weed, also known as filamentous algae, is one of the most common and frustrating issues that pond owners have to deal with. This stringy green gunk can quickly take over a pond, covering surfaces and clogging filters and pumps if left unchecked.
What Causes Blanket Weed? Blanket weed thrives in sunlight, warm temperatures, and nutrient-rich water conditions. Excess nutrients like nitrogen and phosphorus from fish waste, uneaten fish food, lawn fertilizers, or decaying plants feed the explosive growth of this algae. Poor water circulation also contributes to the problem.
Getting Rid of Blanket Weed While blanket weed is nearly impossible to eliminate entirely from ponds with fish, there are ways to control and minimize its growth:
Physical Removal Using a rake, skimmer or pond vacuum, physically remove as much of the blanket weed as possible by hand on a regular basis before it spreads.
Adjust Nutrient Levels Perform partial water changes to dilute excess nutrients. Add barley straw products which release a chemical that inhibits blanket weed growth as it decomposes.
Increase Aeration Install a fountain, waterfall or air pump to improve water circulation and oxygenation which blanket weed doesn’t like.
Use Algaecides As a last resort, algaecide treatments containing quaternary ammonium compounds can provide a temporary chemical control of blanket weed but need to be used cautiously around fish.
Prevention The best way to avoid blanket weed is to follow good pond management practices – don’t overfeed fish, find shady spots for potted plants, use biological filters, and maintain good water circulation.
With some diligence in combining physical removal with creating less hospitable conditions, blanket weed growth can be managed to enjoy a clean, clear pond.
