What is Blanket Weed?

Blanket weed is a collective name for algae as there are over 20,000 species of algae. Although these species of algae are different most will look and behave identically. The most common genera are Cladophora, Oedogonium and Spirogyra. The most common algae we find in our ponds is generally referred to as blanket weed or string algae. 

Algae is a form of plant life that when given favourable conditions, which is generally given via our ponds, is extremely efficient in colonising and dominating. The rapid growth of blanket weed is generally due to the absorption of light and nutrients. 

Can algae kill your fish?

Algae does not pose a direct threat to the health of the fish. In perfect conditions, algae may form a beard-like covering around the sides of your pond which is great for fish such as Koi who will graze on the soft, lush growth. If the algae grows into long strands (like hair) they may be less inclined but may still graze on the weed. Fish such as Koi and Goldfish may be less likely to eat algae if they are fed too much fish food. Any excess food given to the fish that has not been eaten or removed from the pond becomes food for algae. 

Blanket weed can be useful in that it provides the perfect nursery for developing fry as it both feeds and protects. Most fish species will eat their own eggs and fry so blanket weed provides good cover.

The main thing people know about blanket weed is that it is unsightly but surprisingly it can be beneficial as it will actively take up minerals and nutrients from the pond. It would work as the perfect plant filter if only it could be confined to one area. It is also effective in oxygenating the pond, but like all plants it will take oxygen back at night. When you notice buoyant blanket weed during the day this is because with strong sunlight its aerating ability will be so intense that it will lead to it rising to the surface. 

What does it need to grow?

The main three factors that contribute to the growth of blanket weed are as follows:

  1. Clear water - We all want crystal clear water so that we can see our fish and with the use of UVCs we can achieve this. The only problem with this is that sunlight can now penetrate the pond allowing an increase of algae growth. Natural ponds are generally very murky from a combination of suspended silt and single-celled algae. Even with a nutrient rich environment, blanket weed is rarely seen in these environments. With a UV light we are removing this suspended material leaving your pond exposed for the colonisation of blanket weed. 
  2. Nutrients - The algae just needs nitrates and phosphates to satisfy their need for growth and these are readily available in ponds. Nitrates and phosphates accumulate continuously through the breakdown of fish waste, plant debris and uneaten fish food. 
  3. Heat - Blanket weed loves warmer temperatures this is why you will generally see blanket weed growth the greatest in shallower areas. 

How can we prevent it?

Unfortunately there is no miracle cure that will instantly remove algae from your pond. Ponds are not swimming pools, they are not meant to be free from algae. You can control the algae by reducing certain factors, such as sunlight and nutrients.

Reducing the amount of sunlight penetrating the pond can help in reducing the algae growth. You can do this by putting up a pergola or a shade sail. This will also help in protecting your fish from birds. Adding dye to the water can be highly effective as well. H2Blu is a highly concentrated blend of colourants to colour lakes, ponds, dams, fountains, water features and other water bodies with a vibrant natural blue look that is aesthetically pleasing. All aquatic plants and algae need sunlight to grow. Sunlight is used by aquatic plants and algae for photosynthesis. By reducing the amount of light penetration into and through the water column, H2Blu effectively reduces, suppresses and retards submerged aquatic plant and algae growth by inhibiting photosynthesis. H2Blu is designed to screen the light rays which the aquatic plants and algae require for growth. It will affect the growth of all submerged plants.

There are a number of other treatments available for the control of blanket weed. Algaecides tend to be quite strong chemical treatments (which are safe for fish and plants if used correctly) but for them to work properly you need to remove as much of the blanket weed / string algae as you can. This is because the treatment will kill the algae but then this dead algae will sink to the bottom of the pond and then will become food for the next crop. You can use a sludge control treatment to pair up with an algaecide. A product such as Pondzyme or Eco-Fix will eat away at this dead material to help reduce the excess nutrients in the pond. Care must be taken when using chemical algaecides to dose correctly for the volume of the pond. Do not use these strong treatments if you do not have high oxygen levels in the pond (provided by a pump that runs 24/7) as a rapid die-off of algae can severely deplete the natural oxygen levels in the water. There are natural plant-based treatments that can reduce the algae growth over a longer period which will be less likely to cause oxygen deficiency.