Discount Leisure Products Advice

Understanding Blanket Weed Control In Your Pond

Blanket weed can be a problem to control in both new and mature ponds. So what is it?
Blanket weed is a string or filamentous algae (not to be confused with the green algae that make pond water go pea green) have long green strands which generally grow from the sides of the pond. Blanket weed is invasive, often being introduced into a pond by birds, new plants etc. New ponds often experience blanket weed problems because of the nitrates and phosphates found in tap water. Remember, if you have a blanket weed problem it is generally counter productive to empty the pond and start again. The blanket weed will still be on the sides of your pond and will positively thrive when you refill it!

A mature pond will experience blanket weed problems when the level of nitrates in the pond increase or there is an excess of sunlight. As the pond heats up during the day you may find also that “blooms” of blanket weed rise from the bottom of the pond, sinking again as the sun goes in and it becomes cooler. This type of blanket weed is known as silk weed or mermaid tresses. On sunny days tiny bubbles of oxygen attach to the weed and it floats to the surface. The matted clumps exclude light and absorb oxygen from the water and can lead to rapid changes in the pH of the water. This will cause stress in fish.

How can Blanket Weed be controlled?
To find a solution it is necessary to understand just what is happening in your pond. Fish produce ammonia and waste matter and are in effect swimming in there own effluent. Fortunately, there are naturally occurring bacteria which are found in ponds that convert ammonia into nitrite and subsequently into nitrate. In addition, air bourn matter is carried into your pond and plants die back and decompose at the bottom of the pond. The bacteria slowly convert the “sludge” into nitrates. You now have a perfect environment for blanket weed to thrive.

Overstocking with fish, especially koi carp, may be one of the causes. Your filtration system may be large enough for the density of fish in your pond and blanket weed is a sign that the filter is doing its job. The filter is designed to grow copious amounts of bacteria, thereby generating copious amounts of nitrate… which blanket weed loves!

The good news is that blanket weed absorbs nitrates and phosphates more readily than green algae, virtually starving green algae out of existence. This is why ponds with a blanket weed problem tend to have clear water.

There are a number of solutions but do keep in mind that there are numerous varieties of blanket weed and they can become immune to a particular treatment. Do remember that an ultra violet light unit has virtually no effect on blanket weed. It is designed to kill green algae which are in suspension in the pond water.

Before using a natural or algaecide treatment remove as much of the blanket weed as you can from the pond. If you have a pond vacuum remove as much of the sludge from the bottom of the pond as you are able. We suggest that you do not use a net as it will spread the sludge through the pond making life rather unpleasant for your fish.

Natural Blanket Weed Control Remedies.
Adding plants such as water lilies to a pond will lower the level of available nitrogen to blanket weed. They will also provide shade which lowers water temperature (blanket weed prefers warm water). If this fails to work there are a number of natural products on the market although you must be patient as they are slow to work. These include Organic Barley Straw and Extract of Barley Straw.

Barley Straw Extract and Organic Barley Straw. It was found that by placing large bales of organic barley straw into lakes that blanket weed and green (and blue) algae problems were much reduced. The chemical process introduces low levels of hydrogen peroxide (2ppm), this interferes with the algae photosynthesis process and is very complex. However, as a natural product, it is almost impossible to over dose the pond.

Pond Balance and Bio Claire are both excellent natural products. Pond Balance changes the water chemistry whilst Bio Claire is an effective deterrent in that it generates bacteria that break down the sludge on the bottom of the pond. Instead of turning the sludge into nitrate the bacteria generate nitrogen gas which permeates through the water. This deprives the blanket weed of nutrients. Both are slow working (two weeks or so) and monthly maintenance doses are required.

Nishikoi’s Goodbye Blanket Weed is another favourite with our customers. It comes as sachets (8 or 32 to a pack) and one sachet per 1000 gallons has to be placed into the pond or filter every week.

Cloverleaf Blanket Answer is another highly recommended product. It has a unique blend of enzymes to combat blanket weed and is fairly cost effective.

Using Algaecides (a type of herbicide) to Control Blanket Weed
The main advantage of this group of products is that they work quickly to control Blanket Weed. They do not alter the water chemistry but are effective, although it is important to follow the manufacturer’s instructions to ensure that you do not over dose your pond. The down side is that having been destroyed the blanket weed decomposes and falls to the bottom of the pond and produces sediment. For ponds with a bottom drain or where a pond vacuum is used for cleaning, this is not an issue.

We often advise customers with a severe Blanket Weed control problem or have a large pond to initially use an algaecide treatment (cheaper) such as Tap Pond Clear or Blanc Kit Excel and then switch to a natural product such as Bio Claire or Pond Balance as an ongoing preventative treatment.

All of the products offered on our website for the control of Blanket Weed are suitable for fish ponds and will not affect wildlife provided the manufacturer’s instructions are followed. When using blanket weed control treatments care must be taken not to overdose the pond, to ensure that ammonia and nitrite readings are zero and that the pond is well aireated during treatment.