How to Get Rid of Algae in a Pond (Pond Algae Control)

by Tory Jon | Last Updated: September 29, 2022

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UV Pond Clarifiers

Strong ultraviolet (UV) light can damage and destroy algae cells. And UV pond clarifiers work under that principle - they blast pond algae with a strong source of UV light. This "clarifying" process effective gets rid of both green and blue-green algae but is ineffective for larger types of algae like string algae (aka filamentous algae or hair algae).

UV pond clarifiers are available in several different configurations: they are attached to your pond pump or come as part of a pond filter.

Essentially, your pond's pump will circulate the water through the UV pond light, which destroys the algae quickly and easily, thus improving the water quality in the process.

Here's a super quick video of how UV clarifiers work.

One thing to bear in mind is that because UV clarifiers are so effective, your filter may quickly become clogged with dead algae and will require regular cleaning. A small price to pay for an algae-free existence.

There is no need to remove any fish from the pond during the process as UV light does not negatively affect them. UV light does affect harmful bacteria and can even damage and destroy virus organisms, making the water safer for fish to live and swim in. During the summer months, there is no problem leaving the UV clarifier running all day long to keep the algae levels down.

UV pond clarifiers, therefore, offer tremendous benefits to koi pond and other fish pond owners with algae problems – not only can you get rid of the algae, but your fish will stand a better chance of living to a good age than without the use of a pond clarifier.

Pond clarifiers that use ultraviolet light are only effective against these green and blue-green types of free-swimming algae and will not remove or reduce algae like string algae or other larger varieties. This is because string algae will not pass through the filter and will therefore not be touched by the UV light. Other methods must be used to reduce these kinds of algae.

Pond Dyes

In what may seem like a contradiction to UV pond clarifiers, pond dyes are designed to help block out the UV light from sunlight.

Why is this important? Algae use UV light as part of their growth method – the less UV light, the less chance of photosynthesis occurring, the less chance of algae growth. This is different from how a UV clarifier works – pond dyes work like sunglasses do, protecting your eyes from harmful UV rays. A UV pond clarifier is more akin to being thrown into the sun!

Also, unlike a UV pond light, pond dye is effective against all types of algae - even string algae!

Pond dye products are safe to use with fish and other pond life but will not remove a large algae bloom. They are more suited to managing the pond once the majority of the algae has been removed by another method or for keeping small blooms from growing further. Once a pond has been clarified by a UV light as much as possible, it is quite simple to keep algae from returning by the regular use of pond dyes.

Another benefit of pond dye is it makes your pond look beautiful!

Here's a video explaining how to use this product and the different colors available.

Keep in mind, blocking ultraviolet light underwater can harm underwater plant life, slowing the process of photosynthesis significantly.

Therefore, it is best to use when any plants have grown to a large enough size to sustain themselves and provide their required benefits to the pond ecosystem.

Chemical Algaecides

The use of algaecide products in a pond or lake can be a risky business as not all chemicals are conducive to the good health of fish (or other organisms).

In fact, if you've kept koi or other pond fish for a while, you'll be aware that many factors can cause problems for their wellbeing.

Adding algaecide products to pond water that contains fish should be considered a last resort and only really necessary under extreme conditions of algae infestation.

Pond algaecides work by attacking the algae cells and destroying the cell wall. This effectively kills and destroys the algae and makes such algaecides a highly effective remedy to the problem of algae.

Algae blooms can be destroyed within hours or days, but that can come with a price. Although algae will cause many problems, rapidly removing it will also rapidly change your fish's environment. While the chemicals themselves may pose no direct threat to any fish – many algaecides are purported to be fish-friendly – the sudden change could be deadly.

The O2 levels in the pond will become lower as the algae die off, and the dead algae will sink to the bottom of the pond. These dead algae will now begin to decompose. The decomposition process requires – you guessed it – oxygen, further lowering the levels in the pond.

If you only have one or two fish, that will probably be fine. If you have a large quantity or the water is low on oxygen due to other factors, to begin with, your fish are going to struggle to survive as there will not be enough oxygen to support them.

Methods of oxygenation may be employed to increase the levels of oxygen in the water, including pumps, fountains, a waterfall, and pond spitters. However, if you are unsure about the oxygen levels in your pond or think that you may have too many fish to support a drop in the levels, avoid this type of pond algae killer at all costs. There are other methods of removing algae that will ensure that your fish remain alive and well.

Any plants you have in the pond should remain unaffected by algaecide treatments (unless the treatment is poured directly onto them) and will recover quickly as the environment changes.

How to Get Rid of Algae in Pond Naturally

If you're averse to using any sort of chemical or product that you might not typically find in a pond ecosystem, then there are more several natural alternatives to removing algae from your pond or water garden.

In short, you can get rid of and control algae in your pond naturally with manual algae removal, incorporating algae eaters like certain fish and pond snails, and adding aquatic plants, barley straw, and even more good algae to your pond.

These are the best ways to get rid of algae from your pond without harming fish.

Let's take a closer look at these natural pond algae control methods.

Manual Algae Removal

Manually removing the algae by hand or with tools (a rake, for example) is easy, fast, and arguably one of the most common algae control methods. It's not the most pleasant of tasks but does get fast results and is one of the safest algae control methods you can use.

With this technique, you won't be able to remove 100% of all algae in your garden pond but will at the very least be able to improve the appearance of the water and reduce the number of algae present.

It is not necessary to do this with your bare hands, of course, but if you choose to do so, then gloves for protection are advised. With the ability to grip, this is an effective method for removing string algae.

Certain tools like a pond rake may also come in handy when trying to remove string algae from the surface of your pond, especially if you have a larger pond or lake and can't reach the middle with your arms.

If it still sounds like a little too much hard work, an alternative is to use a pond vacuum.

These devices will suck up anything you throw at them, including string algae, blanketweed, sludge, and more. They are more effective, quicker to use, and make the job much easier than pond rakes but do cost significantly more – it's a matter of balancing your budget against the amount of work you want to put in.

They can be extremely effective with larger ponds, but if you are only dealing with a small pond, it might not be worth the investment.

Solely using a manual removal technique will not result in a perfect pond. That said, by removing the algae and then tackling the factors that cause excessive algae growth in the first place (e.g., making sure no excess nutrients are entering the pond), you'll be on track for a much healthier pond.

More (Good) Algae

Just as there are good bacteria and bad bacteria, good algae also exist. Good algae require the same conditions for growth as bad algae, so the presence of good algae will inhibit the number of the bad as they will compete for nutrients.

Well-established good algae will effectively shut out and control bad algae growth.

Commercially available treatments work by introducing a particular type of algae to your pond. They grow at the same rate as any other algae but are often chosen to use photosynthesis earlier in the day than bad pond algae.

This limits the number of pond nutrients available for the bad algae to consume, gradually starving it and preventing further growth. Eventually, all of the bad algae are gone and are replaced by the good algae.

You might think that this just replaces one type of algae with another, but there is a benefit. There are microscopic organisms living in your pond water called zooplankton. While they are not too keen on the bad algae, they are quite happy to eat the good algae, which are called diatoms.

As they are well fed, their numbers will increase while at the same time preventing your pond from becoming overgrown with the good algae. Fish like Koi and Goldfish will eat the extra zooplankton, keeping everything balanced.

Here's a video explaining the process from the recommended Nualgi Ponds.

This is a safe and effective treatment for pond algae control but does not work instantly. Time must be allowed for the good algae to grow and thrive, and so if you're looking for instant results, you may be disappointed.

On the upside, it doesn't involve the use of harsh chemical products and is normally effective within a few weeks. If you can wait that amount of time, it is a good product to choose.

Barley Straw

Barley straw doesn't kill or remove existing algae but can help prevent and control new algae growth. As the straw decays, it will de-oxygenate the water and should be used with care if fish are in the pond – the fish will need oxygen to survive.

The decay of the straw is what helps keep the algae under control. After a few weeks of rotting, humic acid is produced. This reacts with the surrounding water, sunlight and oxygen, and produces a small amount of hydrogen peroxide. This is how the water becomes de-oxygenated by binding oxygen into new compounds. With a high enough water-to-fish ratio, you should not experience any problems.

The amount of hydrogen peroxide produced is usually low enough to ensure the safety of fish but is high enough to control algae growth.

Pond Plants

Pond plants will not instantly get rid of existing algae blooms and are not a quick fix by any stretch of the imagination.

However, a well-planted pond will have fewer algae and less potential for growth. Aquatic plants require the same conditions as algae to grow – sunlight and nutrients. The plants in your pond will compete with the algae for these growth essentials and give the added benefit of releasing oxygen into the pond during nighttime.

This means that your pond water will remain well-oxygenated, which is beneficial to any fish you are keeping.

Some pond plants may be difficult for beginners to look after, but aquatic plants like the Hardy Water Lily and Hornwort are relatively straightforward and provide a good basis to build from.

Pond Algae Eaters

Pond algae eaters, used in conjunction with some of the other natural methods above, are an excellent way to keep algae at bay.

So, what eats algae in a pond?

Many popular fish like koi, guppies, common pleco, and even some pond snails, like the Japanese Trapdoor Snail, like to feed on algae and vegetation.

While algae-eating snails are good to have around if you have algae present in your pond, keep in mind, if you have more snails than there are algae to eat, they will find other food sources and may start feeding on any pond plants you have. And this can be hard to control, as snails can reproduce very quickly.

What About Farm Ponds?

Farm ponds are often larger than your typical backyard pond and may require stronger treatments or larger quantities for that reason alone.

Pond dye products, chemical treatments, and proper aeration are arguably the most effective solutions to get rid of algae in a large pond. And, of course, having a good amount of oxygenating pond plants is an effective means of farm pond algae control, as well.

Farms are a hotbed of nutrients and so keeping fertilizer, animals, and animal feed as far away from the pond as possible will help control algae.

Should I Remove Algae From My Pond?

The short answer is that you can't actually remove all the algae from your pond. No matter how hard you try, there will always be a tiny number of algae in any given pond, and the fact of the matter is, that's fine.

When that tiny amount increases, it starts to affect how the water looks and interfere with the ecosystem that already exists. As algae use nutrients and oxygen to help with growth, there will be a reduction in the availability of these things in the pond as the bloom progresses.

If you have fish or other aquatic life in your pond, they will require their fair share of these things to survive. A reduction could have an adverse effect on the well-being of all the animals in your pond, and so it is wise to keep a check on the amount of algae present in your pond.

As algae die, they will sink to the bottom of the pond and cause a sludge (as well as reduce oxygen levels even further). This will again affect the fish as well as the clarity of the water and may also affect any plants you have in the pond.

Further, you may begin to notice a rather unpleasant smell as time progresses.

Without fish or plants, you may decide to put up with the unsightly growths and strange smells. However, if you want your pond to thrive in the best way possible, it's a good idea to get rid of the algae as soon as possible. The longer you leave it, the more chance it has to build up, and the harder the task becomes to remove it.

What Causes Pond Algae Growth?

Before trying to rid your pond of algae, you should understand what caused the growth.

Why? If you try to control algae in your pond without knowing what caused it in the first place, it will most likely come back.

First of all, algae are present in all forms of water, even water treated at your local water company.

Once your pond water is affected with algae, it will need nutrients to develop and grow.

These nutrients can come from a number of sources, including:

Fish Waste

One of the biggest sources can be waste produced by fish, especially large pond fish like Koi. High-quality fish food will help to alleviate this problem, as lower-quality fish food often contains filler ingredients that the fish cannot process. This leads to excess waste production.

Fertilizers

Other sources of nutrients may include leakage into the pond from external sources. If there is a hole or tear in the pond lining, fertilizers or other nutrients may enter the pond from the surrounding area (check out our guide on how to find pond leaks and quickly repair them).

Further, the use of sprays to help plant growth near the pond may also result in airborne particles entering the water – and if it is good enough to make a plant grow, it will help algae grow.

New Ponds

Established ponds will contain “good” bacteria that require nutrients to survive. These beneficial bacteria will cause no problems for humans or animals and are beneficial to the lifecycle of the pond. And importantly, it will consume nutrients that algae would otherwise consume!

Unfortunately, new ponds will not have this benefit. Fresh, “clean” water will fill the pond and potentially contain algae or spores, and no beneficial bacteria will be present in the clean water to fight against it.

The clear water of the new pond will aid in photosynthesis allowing the algae to grow and reproduce more quickly, while there will also be no beneficial bacteria around that can help to break down and remove dead algae.