Algae control in ponds
There are many different methods through which you can control the algae growth in your pond, and the best results are usually achieved by combining several different methods. It is also important to take the specific environment of your particular pond into consideration before you make any decisions. A type of pond algae control regiment that is ideal for one kind of pond can be highly unsuitable for another.
The first step
The first step in successful pond algae control is to understand what is algae and how algae work. Just like land-living plants, algae need water, carbon dioxide, light, and nutrients to survive. They will also need oxygen just like any other creature, but oxygen is always produced as a by-product of the photosynthesis carried out by algae. Just like a land living plant, living algae will produce more oxygen than it consumes and getting enough oxygen is therefore rarely a problem for algae. (Having a reasonable amount of algae in your pond can actually help you keep the oxygen levels up.)
When it comes to water, the algae will naturally be able to get all the water they need to form the pond itself, and getting sufficient amounts of carbon dioxide is not a problem either since carbon dioxide is exuded by all the living creatures in the pond, e.g. fishes and invertebrates. This leaves us with two factors that can be used for pond algae control: nutrients and light.
Nutrients
A pond rich in nutrients will be able to support a much large amount of algae than a pond where nutrients are scarce. In a garden pond, excess nutrients can, for instance, be a result of over-feeding your pond fishes or not using any filter to filter away organic waste products. In a larger pond, an excess of nutrients can be transported to the water through streams from the surrounding landscape. Ponds located near farmlands where fertilizers are used can, for instance, suffer from immense algae blooms as a result of all the extra nutrients.
Reduce light
Restricting the amount of light that reaches your pond is naturally much trickier than keeping an aquarium shaded. If you plan on digging a pond for your garden, it can be a good idea to place it in the shade since this can have a hampering effect on algae growth. You should, however, keep in mind that garden ponds placed under trees and bushes need to be cleaned more frequently since the falling leaves will litter them and provide them with excessive amounts of nutrients.
Plants
One way of limiting the amounts of both light and nutrients for the algae is to keep your pond heavily planted. Aquatic plants and algae will compete with each other over light and nutrients and a heavily planted pond is, therefore, less prone to explosive algae growth. Using plants for pond algae control is an environmentally friendly method that will work in the long run and make the various "panic treatments" available for pond algae control less necessary.