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One of the greatest problems for the pond owner is algae and green water . There are many different kinds, but they are principally divided into two groups. There are the free-floating and suspended kinds. These are minute single celled species which cause an algal bloom in the pool turning the water like pea soup. Then there are the filamentous types including silkweed, blanket weed and mermaid’s hair. Although rarely a sign of an unhealthy pool, algae can cause the pool owner considerable distress for they completely ruin the visual effect.

Free-floating and suspended algaes of the kind that turn the water green are most common in spring or in a pool that is too rich in nutrients. At the start of the growing season even a well-balanced pool may suffer from a temporary algal bloom as the water starts to warm up. Algae will appear very rapidly in such conditions and proliferate until more developed plants, such as the submerged aquatics, begin to grow actively and waterlilies and other floating foliage plants develop and produce surface shade. Once all the plants are growing freely the nutrients that are causing the problem are mopped up and the algal bloom disappears almost as quickly as it arrived.

It is essential during the spring to be patient and to wait for nature to take its course. Providing that you have a suitable balance all will eventually come right. Whatever you do resist the temptation to empty the pool and refill with fresh water. This produces temporary alleviation of the problem, but after a few days the water will be greener than ever. Never change pond water that is green if you have a good balance of other aquatic life in the pool. Just be patient.

Filamentous algae come in several different forms. The most persistent and troublesome is blanket weed or flannel weed, a thick mat-growing kind that is coarse, fibrous and tangles itself around all kinds of aquatic plants. In bad cases it often forms large floating mats or colonies, often the lower parts in dense accumulations starting to decompose through lack of light and creating an unpleasant smelling brown or black mass. One of the most irritating aspects of blanket weed is that it often grows well in a pond that is otherwise completely clear. Rarely does it seem to flourish in green water.

Silkweed is a similar proposition. This is a more slimy growth which clings around submerged aquatics and the leaf stalks of waterlilies and other deep water plants. It is usually a very dark green and unlike blanket weed, which can be easily lifted from the water by hand, tends to slip through the fingers and is in every respect more difficult to remove.

Mermaid’s hair is quite innocuous. This is the hairy pale green algae which clings to planting baskets and to the walls of the pool and in many cases provides a natural look to the pool. Providing that it does not start to invade the stems of waterlilies or become tangled amongst submerged aquatics it is not a serious problem. However, if you want a crystal clear, perfectly clean pond you will doubtless wish to get rid of it.

The ideal solution for algae control is a biological one. The creation of a balance that will not allow it to develop freely. The principle behind it is that if sufficient submerged plants are introduced to utilise the major plant foods that are available in the water, and enough surface shade is provided by floating foliage to reduce the light falling beneath the water to a situation whereby only the submerged plants can tolerate it, then the water should be clear.

This is a very good theory and for the most part it is successful. However, a pond is a natural and evolving environment and so changes inevitably take place, so constant monitoring is required if a natural balance is to be maintained. Something as simple as introducing a fresh container of aquatic plants in compost which may add a few more nutrients to the ecosystem can be just enough to tip the balance.

The natural way is the best method for coping with algae. Having the right plant balance is the key, but this must link into the sensible introduction of fish such as Koi Their over-population can also quickly tip the balance back in favour of the algae, especially the green water discolouring kinds. If fishbecome a significant interest and you want to introduce more and more then it may be worth abandoning natural algal control and consider a filter. Of course, fresh water mussels can serve as something of a natural algae filter, but do not depend upon them as their activity is very limited. Likewise the ramshorn snail, which will undoubtedly make a contribution, but will certainly not clear a pool of filamentous algae.

It is sometimes necessary to use an algicide to alleviate a green water problem, particularly in a recently established pond where the plants are going to take a considerable time to be functional.Under such circumstances an algal bloom can impair the ability of submerged plants to become quickly established be reducing light levels. Under such circumstances clearing the water temporarily with an algicide will confer significant benefits.

There are mainly two kinds of algicide, each of which must be used with great care, strictly following the manufacturers’ instructions. One is based upon potassium permanganate and is easily recognisable as it is a purplish coloured liquid. This is useful against suspended algae and may cure green water, but has little effect upon filamentous algae. It must only be used when the water is cool otherwise it will turn yellow and the fish will be seen rushing to the surface and gasping for air.

The other kind, which is effective against both filamentous and suspended algae is based upon a formulation of copper sulphate. Never use copper sulphate crystals alone, for although they are freely available and will control algae very effectively, only minute concentrations are tolerated by fish. An excess of copper sulphate in a pool combines with the body mucus of the fish and causes asphyxiation. If used in a proprietary formula it is quite safe and effective.

The only thing to bear in mind is that if there is a large concentration of filamentous algae, that once killed by the algicide it will start to decompose and de-oxygenate the water, and so after treatment has proved to be effective it will still need to be removed from the pond. The difference between taking out dead algae and merely removing the live green on a hooked stick, is that if any small piece of the live remains it will not start to grow and invade again.







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