Does Copper Inhibit Algae Growth in Ponds?

Algae is a problem in most ponds, where it can quickly grow out of control. The worst type of algae will release toxic substances into the water which may harm fish and other aquatic life.

Copper sulfate is used to kill algae because it has an effect on photosynthesis in the algae cells by preventing them from carrying out their process of converting light energy to chemical energy.

Does copper sulfate kill bacteria?

Yes, it also kills bacteria found naturally in pond water that is needed for balancing pond ecology – copper sulfates inhibitory effect on these bacteria leads to an imbalance in bacterial populations, which causes problems such as green or cloudy water and bad odors coming from your pond.

How does copper kill algae?

Copper will kill algae in your pond, as it interferes with the normal process of photosynthesis which takes place in the cells of all plants and algae.  

The blue-green color in the water is a sign that this destructive effect on algae has been successful.

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Copper sulfate works by inhibiting the production of chlorophyll, which is an important component in photosynthesis. Once copper sulfate has been introduced into your pond water, it will positively affect your algae problem within 24 to 36 hours and the algae should be completely dead within 48 hours.

But while copper may rid your ponds of algae, it also does some damage itself…

Copper Sulfate Effects On Ponds And The Plants & Animals In Them

The main problem with using copper sulfate in a pond is the effect on beneficial bacteria needed for maintaining healthy water and aquatic life. In fact, some wastewater treatment plants use copper to kill unwanted bacteria. 

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If you use copper sulfate to clear up an algae problem in your pond, cycles of nitrification will be interrupted.

Will copper sulfate kill fish?

The effect on fish in the pond is also negative according to studies by North Carolina State University who found that:

at low rates (0.05 to 0.25 mg Cu/L) mortality is rapid, with fish dying within 12 hours, but at higher rates (0.25 to 1.0 mg Cu/L) death occurs more slowly over a period of several days.

Copper sulfate is also toxic for any invertebrates living in the water of a pond including shrimp and snails – this means that you should avoid using this product if you are planning to have any fish in your pond because it will ultimately kill them too. 

Copper sulfate should only be used in ponds where there are no fish and any other wildlife such as snails or shrimp. It is not dangerous to frogs, ducks, or swans because they have a higher tolerance of copper than fish.

Can copper damage plants?

One of the side effects of using copper sulfate on your pond is that it kills beneficial bacteria which are needed for maintaining the ecology of the pond. When beneficial bacteria die, algae will start to grow again in your pond and cause further problems as described above.

Another problem caused by copper sulfate is that plants may be killed or damaged by the product as they absorb more copper than algae do because all plants have green chlorophyll in their leaves.

As you can see, copper sulfate treatment of ponds is extremely destructive and should only be used after other methods of dealing with algae such as the use of beneficial bacteria to correct nitrogen imbalances have been tried first. If you DO choose to use copper sulfate, get advice on how to use it correctly to avoid destroying the entire pond ecology.

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How much copper sulfate do you need to treat a pond?

The amount of copper sulfate you need to add to your pond depends on the size and depth of the water body.  

For a small pond, 100 grams (3.5 oz) will be sufficient if the water is less than 1 meter deep. One kilogram would be enough for ponds up to 3 meters deep or larger amounts if needed.

The formula to calculate the amount of copper sulfate you need:

Pond volume in liters x 0.1 grams per liter = Copper Sulfate to add (grams).

Is it really safe?

If you want to use this product, then make sure you get advice from a professional on how to use it in a pond. The reason for this is two-fold: copper sulfate can kill all aquatic life and it also reduces the amount of oxygen dissolved in your water.

If you see any dead fish or other wildlife, then stop using copper sulfate immediately – as it means that they have been killed by its use.

As always, you should also be prepared to do monthly pond maintenance if you want your fish and ponds plants to live a long healthy life.

Finally…

As an alternative to using copper sulfate in a pond, you could always treat a pond with beneficial bacteria. This is much kinder to the environment than using copper sulfate and can even cure algae problems without killing fish and other wildlife.

How fast does copper kill algae in your pond?

Copper sulfate is a very toxic chemical to algae, so much in fact that the dead algae will reduce oxygen levels in your pond.

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To understand if copper kills algae fast or slowly, you need to know how quickly it dissolves and feeds on nitrogen in ponds. 

For this reason, it is important that you apply too little rather than too much copper sulfate.

Remember that in a pond, algae will use the nitrate and ammonia in the water to grow both naturally and through photosynthesis of sunlight or artificial light.

Copper solubility rate is 1-2 mg/L per hr., at pH 6-8 (neutral) or 0.5 mg Cu/L per hour at pH 7.5 (slightly basic).

Low copper solubility is due to the formation of non-ionic complexes with organic compounds and alkalinity. Copper precipitation is caused by low oxygen levels in the water.

Copper does not dissolve below pH 9, so if you have a pond above this level then adding copper sulfate will have little effect on the algae.

At low pH, copper sulfate is very soluble (lots of free ions) and at high ph levels, it is not very soluble.

Conclusion

The benefit of copper in ponds is that it inhibits algae growth. It also helps with the coloration and stability of water, as well as preventing bacteria from growing.

However, there are some things you should keep in mind when using this chemical agent. For instance, copper does not work on blue-green algae because they do not contain chlorophyll like other types of algae (which makes them unable to produce oxygen).

In addition, if used over time or at too high a dose it may result in salt build-up due to its ability to bond with sodium ions which could lead to corrosion problems within your pond’s plumbing system and filter equipment.

References:

Copper Sulfate Toxicity to Various Fish https://depts.washington.edu/wracuw/front%20page/extension_conf/June-8-NAEC-PPT-Freshwater/Straus-Copper-sulfate-toxicity-to-various-fish.pdf

Copper Sulfate – an Often Overused Chemical in Pond Management https://extension.okstate.edu/fact-sheets/copper-sulfate-an-often-overused-chemical-in-pond-management.html