It can be so disheartening to see your lovely new pond turn to pea soup. After you spent so much time and money making it all look nice and filled it with your favourite fish and plants, you at least want to be able to see them.

Well, there is an answer. First however, let me tell you what not to do. Never try to “clean it out”. If you empty the water and replace it you will be back with the same problem before you know it. You will also be putting your fish back into chlorinated water, which can harm them if not left to stand for at least a few days.

The first thing is to understand the problem and what causes it. There are actually two types of algae which are the cause of green water. Free-floating and suspended types that are single celled species which hang in the water and give it its green appearance, and the filamentous types often referred to as blanket weed or mermaid’s hair.

Both types are actually harmless to your fish unless blanket weed becomes so thick that they can become tangles in it. However we as fish keepers don’t want to see it. So, what do we do? Well, let’s take them one at a time.

Free floating algae is most common in new ponds in the spring and early summer. This is because the conditions are perfect for them. They need sunlight and nutrients to survive. In a new pond there is little competition from other plants and in an established pond other plants are still starting to grow. The answer therefore is to ensure that there are plenty of other pond plants to use up the nutrients and to block some of that sunlight. Often, earlier in the year,  just having patience will work. As submerged plants begin to grow more actively and water lilies start to cover more of the surface the floating algae will start to subside.

Filamentous algae, usually present in the form of blanket weed, can be prevented using the same methods as it too thrives on nutrients from fish waste and sunlight. It can be physically removed by using a split bamboo cane or similar implement and twirling round in the weed, literally winding onto the stick from where it can be pulled of and disposed of.

Silkweed is a similar to blanket weed but has a more slimy texture and is often found clinging to submerged aquatic plants, pumps and the water lily stems. It is usually a darker green and is harder to pull out.

Mermaid’s hair is mostly harmless. It is a hairy paler green algae that clings to plant baskets and the sides of your pond. It won’t usually do any harm and can be left alone.

So as we have said, a natural cure is often the best one. However, if this is not working for you or you want to speed up the process of alleviating green water, then you should consider one of the following options: -

a chemical cure such as “goodbye green water” a product made by Nishikoi. This and other treatments is available on the main site page pond remedies and treatments.

a pond pump and filter system – see our pond pumps and filters page

introducing more plants – see here for an excellent choice of pond plants

If you do choose a chemical solution, remember that as your algae dies off, it will decompose in the water. You should bear this in mind and consider a pond vacuum for removing silt and sludge from your pond.

Filed under: Ponds

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