Pond Algae Control Tips

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Written By Mark Washburn

Mark has 20 years of experience as a professional pond management consultant.

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Pond algae control honestly isn’t something that most pond owners think of when they’re first starting out.  Usually, we have visions of a beautiful fish pond full of koi or goldfish, some pristine plants, and a breathtaking waterfall.  The last thing we think of is everything turning green!

The sad reality though is that for many, the fight against pond algae, and learning how to control it is something most people will have to deal with.

Pond algae can show up in many forms but the most common will be some type of string algae, which is thick strands of growth that may extend up from the pond of the pond or spread across the surface.  It would be hard to compare string algae to anything other than maybe spinach which might be good for you, but many people don’t like that either!

Another very common form of algae is green water, which is actually made of up single cell algae of various species.  The color of pond water can vary from a light tinting of green or brown to a heavy, seemingly solid soup of green color.  One would think that nothing could survive in water like this but the fact is, in most cases, fish will do fine.  A pond owner won’t however because they may go months without ever seeing their prized koi.

Algae can be found clinging to the sides of a pond, whether it’s natural or has a rubber liner.  Waterfall rocks are also a prime growing ground even though they may have a constant flow of water running over them.

What Causes Pond Algae?

It’s important to realize that algae is like any plant. It needs certain things to grow well, and if those things are present…well you know the rest of the story.

What we’re talking about here are things like ample sunlight, abundant “fertilizer” or plant food, and relatively warm temperatures. Sunlight and temperature are pretty self-explanatory, but what about the food for algae?

If algae were a vegetable most gardeners would get this one right away and particularly when we start talking about compost. Compost is, for the most part, made up of dead organic material that is slowly rotting away or being naturally broken down into other forms of stuff that can be used, consumed or assimilated by something else. Your pond actually has some compost in it too.

It might be dead leaves, grass clippings, dying pond plants, dead algae and other good things like that. Coupled with the waste from fish, you have an organic cocktail that algae will surely love. And it doesn’t matter if your pond is big or small, the same general principals apply (although fish have much less affect in larger waters).

A Common Algae Treatment

Common sense would usually suggest that the best way to handle an unwanted growth of algae is to treat it like a lawn weed. With those most folks would either pull it out manually or try to kill it in some way, and so it is with algae.

Manual removal is really a safe approach to dealing with string algae (it won’t work on green water obviously) but it can also become quite a chore if the algae is growing quickly. After awhile the ongoing frustration may lead to simply wanting to kill the plant with a chemical known as an algaecide. These usually contain some form of copper or copper sulphate which is toxic to most algea.

There may be times when an algaecide is useful and effective but there are also trade-offs in using them. First of all, as we noted above, it’s organic nutrient levels that greatly determine whether algae will thrive or not and as long as they’re present, algae has the opportunity to grow aggressively. This means that if you take the chemical route, you’ll need to use them often to keep things in check. Normally when an algaecide is applied, algae will die off very fast, and this can pose a hazard to fish. When any plant dies, it will pull dissolved oxygen from the water and the fish need this to survive. And some areas around the U.S. are now banning the use of copper algaecides because of an increase in the metal concentrations in their water systems.

Despite the fact that algaecides may not address the root of the problem of algae, they may have some benefit to controlling spots or areas of growth that may be stubborn. Nature however has a better approach in many cases and that’s by using special bacteria to help break down organic elements in the pond and lower nutrients. This is, in a sense, Mother Nature’s pond cleaning mechanism and it works well if it’s supported and natural algae control is possible.

Most of the bacteria that’s doing the work is aerobic which means in needs oxygen to function. Some ponds have good levels and some don’t, and for those that do not, an aeration kit may be very useful. Coupled with some supplemental beneficial pond bacteria, many ponds can be restored and algae reduced without the use of chemicals entirely.

Small fish ponds benefit greatly from this approach because it’s much safer than using a chemical algae killer. Owners of large ponds can also lose fish because of misapplication of a chemical too, so no one is immune to risk, and therefore, biological tools can be useful on big water as well.

Other Algae Control Tools

In addition to algaecides, beneficial bacteria, and aeration, there are other tools that may help with algae issues. One worth investigation, and particularly if your pond is large, is ultrasound or ultrasonic algae control. This device uses sound waves, specifically tuned to match the vibrational frequency of an algae cell. As this sound wave travels through the water is creates a resonance or vibration in the algae and it begins to break apart.

Ultrasound seems like science fiction but it does actually work and has proven to be effective a good deal of the time. Many industries such as waste water operations are beginning to use it more for controlling algae in lagoons and basins. And pond owners can benefit as well.

Pond dye is another tool that may help with algae problems. Since sunlight is a major support of plant growth, limiting this exposure may reduce algae of various types. It works particularly well on algae at the bottom of a shallow pond.

And finally, many people have heard about, and asked about barley straw. Dried barley straw has been used overseas for many years to good effect and both small and large ponds have benefited somewhat from using it in the U.S. As the straw decomposes in the water it releases several substances which have proven toxic to some types of algae.

Barley straw may not work in every case but when it does it can provide several months of good control and a relatively low cost. The only way to really know if it will be effective in your particular pond is to try it.

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