Best Pond Algaecide and Algae Killer 2023 (Updated)

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Best Pond Algaecide and Algae Killer 2023 (Updated)

Most algae treatments for ponds are designed to remove free-swimming floating algae, but do little to combat other forms, such as string algae and blanket weed. Pond Algaecide treatments are chemically engineered to destroy all forms of algae, making them much more effective. In this article we’ll cover some useful information about the best algaecide treatments, and recommend steps for the safest usage.

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Nualgi Ponds Natural Algae KillerTetraPond Algae Control TreatmentGreenClean Granular Algaecide
GreenClean Granular Algaecide


Is Using an Algaecide Right For Your Pond?

how to remove algae in ponds
Algaecide works to remove all algae, including string algae (blanket weed).

Pond algae, also called pond scum, is one of those things every pond owner has to deal with to some degree. For most of us it never becomes a huge issue, and even if it does, it can usually be remedied effectively with non-chemical based treatments. The problem with these treatments, however, is that they’re generally slower to work, and also do not effectively remove larger types of algae, such as string algae and blanket weeds.

For example, pond clarifiers are a fantastic way to remove free-swimming algae (green water algae) and help control its future growth, but they only target the floating algae particles and will have no effect on other kinds of algae. Since free-swimming algae will be the primary reason you suffer with green pond water, usually treatment with a UV clarifier will be more than enough for most pond owners. With that said, if you also suffer with a lot of string algae, and want to clear your pond with little manual work, a pond algaecide treatment may be a solution to consider.

Chemical pond algaecides, or herbicides, are very effective at what they do, but can also be extremely bad for fish, plants, and pond life. Care needs to be taken during application, and unless you have a major issue with algae and blanket weed, we would recommend other alternative algae treatments in almost all circumstances. Treatment with a UV pond clarifier is easier, safer, and much better suited to small ponds or fish stocked ponds, as there are no chemicals involved that can negatively impact the animals and ecosystem. A combination of UV clarification and manual removal (vacuum/net) should be your first line of defense against algae before considering chemical removal.

For a list of our recommended UV clarifiers to remove algae, check below:

Algaecide Ingredients – How Does it Work to Kill Algae?

algaecide treatment for ponds
Most algaecide treatments for ponds contain an active oxidizer

Most common algaecides on the market work as oxidizers, destroying the cell walls of algae on contact with the substance. These oxidizing chemicals are quick to work,  being capable of destroying almost all algae particles within a very short time window. Unfortunately, you’ll still need to do some manual work with algaecides as the ‘destroyed’ algae particles will remain in your pond after treatment, usually clogging the filter box and settling on the pond floor. Constant and heavy cleaning of this dead algae matter is required in ponds, especially those with fish, as it will eventually decompose and greatly impact dissolved oxygen levels in the water.

Other chemicals include copper based solutions that require a more constant dosing process, but last longer than fast-working oxidizers. With these treatments you maintain a certain level of copper in the pond water which effectively inhibits further algae growth. The problem with copper based treatments, such as copper sulfate, is that they are only good at preventing growth, and not for killing existing algae. This kind of treatment is also very expensive and extremely toxic to most wildlife (snails, insects etc.), so more common oxidizing based treatments are preferred in most cases.

Are Algaecides Safe for Pond Fish & Plants? 

are algaecides safe for fish
Algaecides reduce oxygen content, so directly oxygenating water is important during treatment.

Algaecide treatments can be safe for both fish and plants if used correctly, but there will always be a risk factor involved. The chemicals in algaecides, although potent, do not directly harm your fish on contact when dosed correctly. Instead, fish that usually die from the use of algaecides in ponds die from the extremely low oxygen levels after and during treatment.

When the algae dies it begins to decompose with the help of beneficial pond bacteria, and these bacteria use large amounts of oxygen during the decomposition process. If you have fish and plan to use chemical algaecide treatments, you need to heavily aerate your pond water to prevent risk of suffocation due to lowering oxygen content.

If you cannot effectively aerate a fish stocked pond, do NOT use a chemical algaecide. Likewise, if you have a very heavy stocked fish pond, using an algaecide even with heavy aeration can still carry a risk as the fish will also be consuming a large amount of oxygen alongside bacteria. For heavy fish stocks, you’ll need to carry out both heavy aeration and a strict cleaning procedure throughout the treatment to ensure safe water parameters.

How to Use Algaecides More Safely with Fish:-

1) Consider treating your pond in sections

Splitting your garden pond into quarters and treating the water in segments is good practice to avoid over treatment and poor oxygen levels. After treating one section, you can wait 7-10 days for the water to re-balance and determine if a second treatment is required. If it is, treat the second section and repeat the process until algae is under control. Allowing time between each treatment provides your pond an opportunity to re-balance and regain normal oxygen levels. 

If you’re treating your pond in summer, remember that warmer water = less dissolved oxygen. Care needs to be taken especially in warmer months, and treating in sections will help minimize stress of oxygen and fish. Adding a dedicated air pump as an aerator is still essential if you have fish, regardless of how you decide to treat.

2) Add an air pump during treatment for oxygenation

A great way to maintain a safer level of oxygen during treatment with an algaecide is to add an air pump or aerator to your pond. This is especially important if you have a fish stocked pond, as low oxygen levels will place a huge amount of stress on your fish. Aerators can  include waterfalls, fountains, or even air pumps which mechanically pump oxygen into your waters. If you don’t have a strong waterfall or fountain, or if you want the safest conditions possible, adding a air pump with diffuser is the best way to oxygenate.

3) Make sure you clean your filter frequently

Algae that dies during treatment needs to go somewhere, and it will either end up on the bottom of your pond or in your filtration system. Depending on how much algae you have in your pond, frequent cleaning may be required to ensure your filter is working optimally during treatment. Smaller filters can quickly become clogged and ineffective if not maintained, so make sure to open your filter daily and check the media. Bacteria inside your filter will work to break down dead algae but it can only handle so much at once, and if it becomes clogged it won’t be getting sufficient oxygen to work effectively,

4) Remove debris and bottom sludge during and after treatment

how to remove pond sludge
After treatment, any sludge and dead algae needs to be removed.

Any dead algae that is not sucked up into your filter will eventually settle on the bottom of your pond. This will begin to decompose and release harmful substances, such as ammonia and nitrites. These compounds also contribute to the growth of very thing you’ve just removed – the algae! After and during a treatment, it’s good practice to manually remove the heaviest of debris from your pond, which can be done easily with a rake or pond vacuum cleaner. If you suffer with a lot of bottom sludge, you can also consider adding a natural bacteria based treatment which helps break down the sludge naturally over time. Sludge remover treatments work best when coupled with a vacuum cleaner, as they take a long time to become effective.

5) Add activated carbon after treatment to remove residue

does activated carbon help control algae
Added activated carbon after treatment can help neutralize any other pollutants and chemicals.

After a treatment has ended, you can add a extra layer of filtration to your system called carbon filtration. This type of filtration, which comes in the form of activated carbon (charcoal), is designed to remove harsh chemicals and organic pollutants from your pond water that normal filter media cannot. These chemicals include perfumes, pesticides, acids, and algaecides – all of which can be neutralized with frequent dosing of activated carbon. Once you’re happy that algae is under control, adding activated carbon to your filter in a mesh bag will help remove any left over residual chemicals left behind after treatment, and allow your pond an easier recovery.

6) Follow the products instruction label EXACTLY as directed

A final and somewhat obvious final step is to ALWAYS read the instruction label of the algaecide treatment you’re using! More often than not we see pond owners who have killed their fish because they haven’t properly followed the instructions. Take note of each step, and make sure the dose is correct for your pond’s size and fish stock levels. Everything should be clear on the label of the product for a safe treatment process.

Natural vs Chemical Algae Control – Which is Better?

Nualgi ponds bacteria based natural algae remover.

Chemical algaecides are extremely effective at quickly killing all kinds of algae, but there are also natural algae treatment options available that are slower to work, but much safe for fish and plants. Depending on the level of algae you have, and how dense your fish stock levels are, a natural treatment may be a better option.

With that said, natural treatments still reduce oxygen levels, just not as quickly as chemical algaecides. As algae dies and begins to decompose, oxygen is used by bacteria and ammonia and Co2 are released. Even when using a natural algae control treatment, we would still recommend reading through and applying the steps above to ensure your fish are safe.

The key takeaway for natural algae products is how fast your algae is growing and what kind of algae you have in your pond. For example, these treatments are not usually as effective on string algae and blanket weed, so this needs to be taken into consideration. They will also not remove a heavy algae bloom as fast as chemical algaecides or some powerful UV clarifiers.

The Best Algaecide for Ponds Review 2023

Chemical algaecides should not be used in ponds that are not efficiently aerated. They should also not be used in heavy fish stocked ponds, or in ponds with weak/sick fish. Care needs to be taken on application, and manufacturers dosage instructions followed exactly as described on the product label.

Natural Algae Remover

1) Nualgi Ponds Natural Algae Control Review

An interesting natural algae remover which promotes the growth of silica-body algae called diatoms, which actively starve and compete with nuisance algae in your pond. This product is especially effective for ponds which contain fish, as the purpose of replacing one type of algae for another is that the new type is a favorite food for your pond’s zooplankton. These are tiny micro-organisms that live in your pond and consume organic material, such as plants. As the number of diatom algae grows, so does the zooplankton population, and these can be then eaten by your pond fish – thus enhancing the natural food chain.

Zooplankton much prefer diatom algae to regular green water algae, and as this silica based algae begins to grow, it will slowly starve the rest of the algae of the nutrients it needs. It does this by photosynthesizing earlier each day in comparison with normal algae, competing directly with the algae and eventually outgrowing it.

As well as this, the formula actually increases oxygen in your pond and helps with nutrient balance. Diatoms release oxygen as they grow & consume CO2, thus increasing dissolved oxygen levels.

The downside of this algae remover is that it is slower to work compared to chemical algaecides, and works best against regular free-swimming algae. We found that it was not as effective against large string algae and blanket weed, and required a lot of time to become established. If you have a lot of string algae we recommend manually removing it while Nualgi helps reduce regular algae populations. For maximum results, you can combine Nualgi with a dose of beneficial pond bacteria that will work alongside the product to break down dead algae and improve water clarity.

Overall, this is an effective algae control method and would be ideal for highly fish stocked ponds. It is 100% safe for fish, and having fish means they will consume the extra zooplankton as the new diatom algae grows. One of the best pond algaecide treatments for the natural removal of green water!

  • Type: Natural Algae Remover
  • Works against: Free-swimming algae
  • Active Ingredient: 12 essential nutrients to promote diatom algae growth

Chemical Algae Remover

2) TetraPond Algae Control Treatment Review

A chemical algaecide with a powerful active oxidizing ingredient that quickly destroys free-swimming and string algae. TetraPond’s Algae control treatment has been designed to be fish and plant safe, but precautions still need to be taken. As this is a chemical algaecide, it will place huge stress on your fish if your pond is not heavily aerated. If you don’t have a method of natural aeration, such as a fountain, we strongly recommend an air pump during treatment. If you have no fish in your pond, the treatment should have no ill effects on your plants if proper dosage instructions are followed.

The active ingredient is a strong oxidizing agent that quickly kills algae and removes green water on contact. The dead algae will then sink and need to be removed from the bottom of your pond, and your filter media regularly cleaned. This is especially true if you have fish, as decomposing algae reduces oxygen and releases CO2.

The treatment is effective against a large range of algae, including string and blanket weed. For most ponds you should see complete removal after a single dose, but larger ponds with more algae bloom may require an additional one after the pond recovers. If you have a heavy fish stocked pond, you will need a very heavy aeration system in place. If you do not have adequate aeration, we do not recommend this product!

Overall, a strong and effective algaecide for ponds with medium-heavy algae growth. Will work on most types of algae, and is safe for fish and plants so long as proper dosage instructions are followed.

  • Type: Chemical Algaecide
  • Works against: All types of algae
  • Active Ingredient: 5.4% Poly [Oxyethylene, (Dimethyliminio) Ethylene (Dimethyliminio) Ethylene Dichloride]r

Chemical Algae Remover

granular algaecide for ponds3) GreenClean Granular Algaecide Review

Another chemical-based algaecide treatment is GreenClean’s Granular Algacide. This specific formula is granulated and designed for the most efficient elimination of string algae close to the surface of the pond. The active ingredient is a strong oxidizing agent, and will destroy algae on contact. The product is EPA approved, USDA National Organic Program compliant, and safe for fish and plants when dosed correctly.

As this is another chemical algaecide, if you’re treating a fish stocked pond, it should only be used in heavily aerated pond systems. Just like TetraPond’s product, this will quickly deplete oxygen levels in your water, which can have a negative effect on fish if used incorrectly. Having a natural aerator, such as a fountain, or adding an air pump and running it 24/7 will help increase pond oxygen levels.

The product does fast work and kills algae within minutes, and you should see dead algae begin to float which need to be constantly removed. If left, the algae will eventually sink and start to decompose and reduce oxygen levels – which needs to be avoided!

This particular algaecide has very good consumer feedback, but is only recommended as treatment against string algae. It will kill all forms on contact, but its granular structure has been designed specifically for string algae removal. If you’re treating a pond with no fish, your plants will not be negatively effected if dosage instructions are followed.

Overall, a very effective chemical algaecide which works very quickly to eliminate string algae from pond water. It is considered safe for fish and plants as long as dosage instructions are followed as per manufacturer’s recommendations.

  • Type: Chemical Algaecide
  • Works against: String algae
  • Active Ingredient: 42.5% Sodium Carbonate Peroxyhydrate


8 thoughts on “Best Pond Algaecide and Algae Killer 2023 (Updated)”

  1. Hello can you recommend an algae killer I have put two different algae killer but non have got rid of the algae. I have a green genie it only brings it to float on the top. The algae you can’t scoop from the top in a net as it just disappears. Heavy rain makes it comes to the top then it sinks to the bottom. What can I do many thanks yours sincerely Brenda Russell

  2. We have a 3 tiered waterfall pond with a lot of green string algae that we can’t get rid of . We don’t have any fish but we do have a large Rottweiler that jumps up and sets in the middle tier to cool his stomach. Not sure that he drinks any of the water, but wondering if the Green Clean Granular Algaecide would bother him?

  3. Have had my 600 Gallon pond now for 2 years just lately getting String Algae growing and only in the water fall, PH 8.4, KH 150ppm, all other Water parameters Normal.
    What do you suggest as best treatment?
    Chemical treatment with on of the a bow mentioned Product
    Summit 130 Clear-water Barley Straw Bales.
    Liquid Barley.

  4. I have a 60,000 gallon natural pond on my property, it does have fish and wildlife drink it. The algae and floating muck has taken over. I really need help on what to use to get rid of the algae safely and fast, any suggestions. Thank you

    • Hi James,

      Sorry about the delayed reply! Algaecides can work for a quick fix when things are bad, but we highly recommend utilizing a beneficial bacteria supplement as these will work to naturally break down algae, sludge, and other organic matter and will keep working for many months. After adding beneficial bacteria, you may notice the water become cloudy – this should clear up after a few days to a week, and is completely normal as the bacteria colonize and get established! Before adding the bacteria, try to manually remove as much of the floating muck as you can with a net or rake so that the bacteria can work faster.

      If you’d like more info on beneficial bacteria, we have a couple of articles devoted to this topic:

  5. Hi there, my husband and I are purchasing a piece of property with a natural pond on it. As far as I can tell there are no fish in the pond- the surface is totally covered with pond scum. Pond is about a fifth of an acre and up to six feet deep. I realize this will be a process, but I’m thinking 1) use strong algae killer first, then 2) use. Sludge remover after? The pond is too large for us to manually remove the dead algae. Any thoughts or info you have is appreciated!!

    • ***Also, we prefer natural methods if possible. Eco friendly is good! But I realize this might be past that point as well and might require chemicals- which we will use if we need to. Thank you so much for your help!


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