Fish Ponds

There are various types of algae. There is one that turns some aquariums red and another type of algae we are all familiar with, which most people don’t even realize is algae, and that is seaweed. Another type of algae that comes in large strands is commonly called blanketweed. This incorporates fine particles of silica, or sand, out of the water, making it very tough. Most fish can’t eat it, but grass carp are said to be able to tackle it. Most fishponds get infected with it at some time, as it can be on shop bought plants, or introduced by ducks and other birds on their feet.

Blanketweed is best described as looking like green candy floss. In the water it looks a lot of material, but when you get it out it looks a very small amount. It will choke lilies and oxygenators and also block pond pumps. You can remove some of it by twisting a bamboo cane in it, or you can buy a special tool for the job. The only way to deal with it permanently is to poison it with a selective weed killer. This is not as dangerous as it sounds to fish and other life as long as you follow the instructions carefully.

Algae magnets are another way of reducing the problem. They consist of a large permanent magnet that ionises the water as it passes through it. This prevents the blanketweed from growing, or so the theory goes.

The type of algae that all fishpond owners are familiar with, is the single celled variety that causes green water. In the Winter, when it is cold and light intensities are low with shortened daylight hours, the algae, like most green plants, does not grow, so fishponds become clear. But as Spring comes and everything comes to life, the pond often goes green. This is due to the availability of minerals in the water from decaying vegetation and fish droppings etc. There are several ways to clear green ponds. The most healthy and natural way to do it is to cut down on the fish food and put some more plants in the pond. Oxygenators are available in several varieties and are quick growing, so they are one of the best plants. When the weather is warmer water hyacinths, lettuce and chestnuts are also very useful. Duckweed and fairy moss will help clear the pond, but can become a nuisance in their own right as they will cover the whole pond in a few weeks if allowed to.

A properly installed biological filter is a very good solution to clearing green water. This works by physically removing the particles of muck floating in the water with foam sheets, or filter brushes. Also it has a media in it that has a large surface area for bacteria to live on. These nitryfying bacteria feed off the chemicals in the water thereby removing the food that would have allowed the algae to grow.

The addition of an Ultra Violet system will give clear water as this sterilizes the water when it passes through it thereby killing the algae. They are very good, but don’t remove the cause of the problem, that is free minerals, so it is recommend that a biological filter is used as well. There are many chemicals called algicides that kill the algae and give clear water, but the effect is only temporary and you always have to repeatedly dose the pond every few weeks.

One new method of clearing green water in a pond is by using a small quantity of Barley Straw. A few retailers sell this, but you can often buy it in small packets by mail order and other types of straw will also have a certain amount of success.

The straw is tied in a bundle and immersed in the pond where it slowly decays. Research has not shown conclusively whether it is the bacteria on the rotting straw, or a chemical that is called Hydrogen Peroxide that is released from it, into the water, that clears the pond. However, it will keep the pond clear for many weeks until the straw has become too rotten and then it has to be removed otherwise it will rot further and pollute the pond.

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