Control Algae in a Fish Pond - FAQ

What is algae?

“Algae are photosynthetic organisms that occur in most habitats. They vary from small, single-celled forms to complex multicellular forms, such as the giant kelps that grow to 65 meters in length.. The US Algal Collection is represented by almost 300,000 accessioned and inventoried herbarium specimens.” Quote taken from the National Museum of Natural History website: nmnh.si.edu

What are the common types of algae that occur in your pond?

Most ponds have several species of algae. They include green algae, (which is such a large group I will not bore you with the details, just point you to berkeley.edu where you can spend the next 10 hours reading!), brown algae, and blue/green algae.

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How does it get there?

Most algae starts life as single-cell organisms, so they come in the water itself or are carried by the fish, birds, insects or mammals that frequent the water.

Why does it grow?

Algae, like all plants, uses the nutrients in the water and sunlight to produce photosynthesis and grow. It thrives in water that has high concentrations of nitrates and silicates and waste matter along with strong sunlight or long periods of daylight.

We now know what it is, how it got there and why it grows, so what can we do to reduce it? The key here is water quality. I haven't spoken to the almighty about regulating daylight hours, but you're welcome to try! However, some things are beyond our control, daylight and sunlight being two of them, but we can reduce the effect by careful location of the pond initially. Placing it in a shaded area will cut down the amount of sunlight it receives, but shade may come from trees and shrubs that can deposit leaves in the pond, increasing the amount of waste matter, so regular cleaning is important.

Water quality is the one thing we can control to a great extent. The addition of a good quality filter for your pond will go a long way to improving the quality of the water, in the same way as it does for the aquarium indoors. Pond filters are not expensive any more, and can be purchased for a few dollars. The installation may be more expensive than the filter itself, as it requires power from the mains supply and depending on the location of the filter from the pond, it may require a good length of piping. When you buy the filter, you will also need to purchase a pump capable of handling the volume of water recommended for the filter. This needs to be capable of handling solids too, since the bottom of ponds tend to silt up over time and dead leaves can easily choke the intake. It is better to have them drawn into the pump, where they will be shredded before being pushed into the filter. Modern pond filters are designed to be unobtrusive and most are buried to ground level, so all you see is the lid, which makes them much more acceptable than they used to be. Once it's fitted, you will need to maintain it regularly, as per the manufacturers instructions.

You also need to change the water like you would with an aquarium. The same rules apply to most ponds as they do to fish tanks in your home. A pond is a closed environment, just like a tank, only bigger and outdoors. This just makes it more difficult to regulate and more likely to be forgotten! Unless you have the luxury of a stream running through your garden, the pond is reliant on you to maintain it. Water changes need to be large, around 30 - 50% and regular to keep nitrates down, cleaning needs to be done at least twice a year on larger ponds and more often on smaller ones. Don't think that during the winter the pond will hibernate. It won't, even if the surface ices over, there is still life below the surface, albeit slower than during the summer. If you have a pond filter, care needs to be taken during cold periods to ensure that it doesn't freeze. the best way to stop water from freezing is to keep it moving, so don't be tempted to turn the pump off when the winter comes.

By taking the actions detailed here, you should be able to at least reduce the growth of algae. You will still need to remove it periodically by hand, but there shouldn't be as much to remove. There is one other addition you can make that will help. By the addition of a UVC inline with the filter, the algae spores will be killed off. It won't do anything for the existing algae, but will inhibit the new growth substantially. Be sure that you buy one large enough for at least the capacity of the pond, preferably buy one twice the size of the recommended strength. This will, within a couple of weeks, eliminate the green water problem that most ponds suffer from, and with continuous use, will stop it from re-appearing. It also helps to combat diseases that are water-bound, as it sterilizes the water that passes through the chamber, including disease spores.

There are no guarantees with nature, and this may not help in your pond, but unless you try, you'll never know. The one thing that is for sure, is that the inhabitants of the pond will benefit from better water quality, so be prepared for a population explosion!

Enjoy!