It is one of the most common complaints heard in the Koi industry, “I cannot get rid of this rotten blanket weed.”
We have all been there and it is a really demotivating element of Koi keeping, not to mention time consuming and potentially fatal for our Koi. Back in issue 2 of the magazine Koi Talk we delved deeper into this frustrating aspect of the hobby, what to look for and more importantly how to control it. Here’s a short blog based on the article if you’ve not read it in full yet.
Blanket weed, also known as filamentous algae, is one of the most frustrating aspects of Koi keeping. While it can be a real nuisance, it is important to understand that algae and blanket weed control the water quality of your pond and are often a sign of healthy water. Therefore, it is more important to get the right biological balance in your water so that they do not become non-controllable blooms. This blog post will delve deeper into blanket weed, what it is, how it grows, when it blooms, and its effects on your pond and koi. Additionally, treatments for blanket weed will be explored.
Algae are very primitive plants without roots, and blanket weed is a type of macro algae that create the ‘green soup’ in our ponds. This falls under the Cladophora species genera and is the most common green algae in the world. It was discovered by the German Botanist Friedrich Kutzing in 1843 and today there are 400 species recognized. Normally you can find this in fresh and brackish water and in the sea, which can grow in low and high nutrient levels in the water. Blanket weed uses a complex spectrum of nutritional strategies combining photoautotrophy and heterotrophy. Most koi keepers would consider that blanket weed is a phototroph and depending entirely on their photosynthetic apparatus for their nutrient uptake by using sunlight as the source of energy and carbon dioxide as the carbon source to produce carbohydrates (sugars) and adenosine triphosphate.
The blanket weed cells have N-reducing enzymes so that the nitrate would be reduced to nitrite and then reduced to ammonium. In recent studies, they have found that urea that our koi produce and nitrite or a combination can be a nutrient source too. The bloom of blanket weed occurs in general in the spring and summer when the water heats up by the sunny weather. Through feeding our koi we add nutrients in the water that can accelerate the blanket weed growth. Generally, it is competition for the nutrients that can be taken up by plants or converted by bacteria. Most of the time, they are slow starters in the spring that would increase the nutrients and the opportunist like blanket weed, or algae would outcompete them.
The carbon dioxide uptake can lead to very high pH and oxygen fluctuations. Oxygen levels in the pond can be very high in the day when the sun is at its brightest and in the evening, this would be reduced when the chloroplast needs this combined with the sugars. This leads to low levels of oxygen early in the morning and your koi can suffocate via a lack of oxygen. Therefore, as a rule of thumb always measure the oxygen levels in the morning if you can. Blanket weed is well known for blocking pumps and filters which can lead to poorer water quality. Blocked pumps could mean nutrients are not delivered to the bacteria in the biofilm which is our engine room for healthy pond water. If you have plants in your pond, then the blanket weed has the potential to suffocate them and outcompete them with the nutrient uptake.
There are many different types of treatments for blanket weed on the market, but the general rule is to start early in the year with your treatments. Before you start with a treatment ensure that you remove as much as possible by hand, stick, or brush in order to minimize the treatment needed. When the treatment is active the blanket weed dies and releases the nitrogen that it holds and increases the load on the bacteria in your filter, so bacteria needs to multiply quickly to overcome this load and this will reduce the amount of oxygen in the water.
The first group of treatments would be based on reducing the amount of sunlight that penetrates the water so that the blanket weed would not get their energy source.
Read this fascinating article in full in Koi Talk Magazine, Issue 2.