Snail control & Copper
Snail control & Copper

Snail control & Copper

Uses and risks of copper sulfate to treat snail infestations in the freshwater aquarium.

Text by: Alfredo Franco Cea / Username: alfcea


Many of us know the story first hand. You get the new, exotic plant that you were looking for to embellish your freshwater aquarium and bring it home. After a good rinse, you chose the best spot for it and plant it. A few days later you find a snail… and a few weeks later there are many, many more…

There are many ways to treat a snail infestation which are very well described elsewhere on the internet. However, here I would like to discuss the use of the chemical known as copper sulfate pentahydrate (CuSO4•5H2O). Copper sulfate is a compound that has been used for a number of plague treatments. It is an algaecide, anti-bacterial, anti-fungal, works on external protozoa such as ich and serves many other purposes too. However, it is also toxic to many other living beings and that includes other invertebrates, plants and fish.

Yes, copper sulfate is very highly toxic to invertebrates such as crab, shrimp and oysters. If you have any of these in your freshwater aquarium, you should not use copper sulfate to treat a snail infestation because they will die too.

Yes, copper sulfate is toxic to plants. It disturbs photosynthesis and can kill some varieties. Nonetheless, some species are more resistant towards copper than others. Both Vallisneria sp. and Sagitaria sp. are known to be very sensitive to copper, but Anubias sp. and most mosses will survive a treatment with copper at the recommended doses.

Yes, copper sulfate is toxic to fish. That being said, however, at the correct concentrations, CuSO4 is safe to use in a community freshwater aquarium provided it is used correctly. I, myself have used in my tank without any losses of fish and, though I agree that it is risky, I also believe that a treatment with copper sulfate, if done properly, can be used to greatly reduce a snail infestation.

Vertebrates, like fish, are much more resistant to moderate concentrations of copper ions than invertebrates like snails. Snails are extremely sensitive to copper sulfate. In fact, concentrations as low as 0.01 % kill all the snails present in any body of water in less than two hours. Moreover, recent research carried out by the National Warmwater Aquaculture Center in Stoneville, MS, showed that concentrations of up to five parts per million (5 ppm) of copper sulfate would not kill catfish in outdoor ponds while killing more than 90% of the snail Bolbophorus sp. These concentrations, however, are much too high for a typical freshwater aquarium and should not be used.


It is well known that the lethal dose 96hr-LC50(20C) for pond snails is 0.39 mg/L (or 0.39 ppm). This means that a concentration of 0.39 parts per million of copper sulfate in your tank will kill half of the snails present over a period of 96 hours if the temperature is kept constant at 20 ⁰C (68 ⁰F). This number is a good place to start. This concentration will not harm any healthy fish, but will kill half of the snails present. Pretty good, isn’t it?

Now, if we double the dose, will the massive death of snails occur faster? Will it be a larger die-off? The answer is, probably both; however, this is not recommended at all, since a larger dose will become much more toxic to the other organisms in the tank than two normal doses at different times, when most of the copper has already been removed from the system (more on that later). Always remember that there is not a normal linear relationship between the dose and the effect. A double dose will have a toxic effect much larger than twice a normal dose. Doubling the dose is, therefore, greatly discouraged. At this point it is important to make it clear that, in very large systems, the use of low copper concentrations maintained for a longer period of time might be more effective to control a snail infestation than a higher concentration for a shorter period of time.

It is usually agreed that safe concentrations to use in a typical freshwater aquarium are in the range of 0.15 to 0.2 ppm (or 0.15 to 0.2 mg/L). Any higher may leave the fish with red sores on their sides. However, these numbers have to be taken with care because there are other factors that influence the toxicity of copper ions: The temperature, the alkalinity and the hardness of the water. Copper is much more toxic at higher temperatures than it is at lower temperatures. In fact, for some species of snails, the toxicity of copper sulfate (measured as mortality) increases more than four times when increasing the temperature from 15 °C to 20 °C (59 °F to 68 °F). If you are treating your tank with copper sulfate, try to maintain the temperature at about 22 °C or 23 °C.

The other factors that greatly influence the toxicity of copper ions are the alkalinity and the hardness of the water. In water with a high pH (high alkalinity) and high hardness, the copper ions are sequestered (inactivated) and the effectiveness of the treatment will be reduced. On the other hand, if your tank has very soft, acidic water, the toxicity will be enhanced and many people discourage the use of treatments with copper in these tanks because of the great risks associated with it. In my opinion, however, if you are determined to use copper to treat a tank with soft, acidic water, it is best to start off with a very small dose (about half of the recommended dose) and go from there.


Once you have determined that you will treat your freshwater aquarium with copper ions, the first thing to do is to get it. Some people add copper containing coins or even copper wire to the tank in the hopes that this will release a small amount of copper ions into the tank. This procedure does not work. Metallic copper is completely inert. It will not dissolve in water, will not release any ions and overall will not be effective. It also can be very dangerous because the surface may be coated with harmful bacteria and other parasites that will get into your tank disturbing the equilibrium and, in the worst case scenario, lead to disease and death of all the living organisms within it. Do not do it.

There are two main sources of copper sulfate to treat your tank with. One is from commercial products sold in local fish stores specifically to treat snail infestations. These are very easy to use, since the CuSO4 is already dissolved in water at a safe concentration. Follow the directions in the bottle precisely and you should be seeing a massive die-off of snails very soon. One very common brand has what many people believe to be a “wrong”, “misleading” or “confusing” label. While one label claims the product to contain 3.8% copper sulfate, another label on the same bottle indicates 1.61% copper. This is not a mistake and it just indicates that not all the weight of the copper sulfate is copper (after all, the sulfate part of the compound has some weight too!). By the way, if you follow the directions correctly, you should end up with a concentration of copper sulfate of about 0.2 ppm in your tank.

The other source of copper sulfate is from hardware stores (gardening section- treatment for pests and fungal infections in plants) or even in pharmacies as a disinfectant. It is sold as a blue powder or blue crystals. Both are the same and work well, though the crystals will need to be crushed before using them in the tank as even the smallest crystals contain much more copper sulfate that it is necessary to treat large tanks.

Since CuSO4•5H2O is a naturally-occurring inorganic salt and copper is an essential trace element in plant and animal nutrition, it is usually very cheap. It may be sold under the name of “bluestone”, “blue vitriol” or even “blue copperas”. If you decide to use this source of copper sulfate, do not get too much. You will only need a few milligrams of the powder to treat large tanks. You will also need a balance capable of weighing out very small amounts of solids. If you do not have access to a small enough balance, I would highly recommend the use of some of the available commercial solutions. Adding too much copper will be dangerous to the life in your tank.


Since CuSO4 will kill some of the nitrifying bacteria residing in your filter, the first thing to do when treating your tank is to take the filter off the tank. You can let it run in a bucket of water to keep the bacteria alive and well.

If you are adding a commercially available product, follow the directions in the bottle to add the recommended dose. If you are using the solid (powder) add 0.2 mg/L or about 0.8 mg/gallon. These are very small quantities. If you do not have access to a balance that will allow you to measure these quantities, do not try to guess because the end result may be a large overdose.

After you have added the chemical, you need to stir the water so that the concentration of copper is the same throughout the tank. If it is possible to increase the aeration of the tank without having the filter on, do it. The increased amount of oxygen will help with the depletion of oxygen that will be caused immediately by the massive death of snails. Let the chemical act for overnight. Many people claim that after adding the copper sulfate, they can see many snails climbing up the water column. I have never seen this, but it is very possible. If this happens to you, you can just fish out the snails that come up to breathe (yes, most pest snails have lungs and breathe air) and take them off your tank.

It is possible that you do not see a massive die-off of snails after one night. This will most likely be due to the hardness of the water. Add more copper sulfate in small increments (about 20% of the initial dose) until you finally get the snails to die.

The next day it is very important that you remove all the dead snails that you can find. Look in the gravel and under any decorations because many of them may remain hidden. Then, perform a large water change (50%) and rinse all the decorations with clean water. This is extremely important because the decomposing snails will change the chemistry of the water forming large quantities of ammonia and other toxins that will be more harmful for the fish than the copper itself. Keep the aeration up. This will help oxidize small amounts of toxins that may be forming in the water as the snails die and their bodies start decomposing. The aeration, however, is by no means, a substitute for the water changes.

After three or four days, perform another 50% water change and, if needed, add another dose of copper sulfate (50% of the initial dose). It is important to make clear that although copper sulfate will kill most of the snails present, it will not kill the eggs, that will remain viable and therefore any eggs that had been laid previously will hatch within the next few days. If you need to, it is recommended that you treat your tank again within two weeks of the initial treatment to kill any newly hatched snails. During all this time keep the filtration system off, but also keep very good aeration. Perform large water changes every few days for two weeks.


After two weeks of large water changes from the last addition of copper, it is time to completely neutralize the remaining copper. Since copper is an element, it cannot be decomposed into simpler, harmless substances and it will remain as is, for ever. The only known way to eliminate copper is by doing water changes. Still, unless you do a 100% water change, some copper will remain in your tank. Since copper is an essential trace element in animal and plant nutrition, very small amounts of it will not be harmful at all, but at this point you probably will have more copper in solution than the recommended “trace element” dose.  At this point you can start the filtration system again and, if it has some activated carbon (charcoal), it will be helpful in eliminating a little of the copper still remaining in solution. This will not be a definite procedure and you will still need to deal with the remaining copper ions.

There are two ways of inactivating the residual copper that will still be lying around in your tank. One is increasing the pH and hardness of the water, which will form an insoluble solid that will be harmlessly lying at the bottom of the tank and will be eventually removed by gravel vacuuming. This is not very recommended because, that will be making use of more chemicals that could make more harm than good, unless you know exactly what you are doing and how to deal with any possible eventuality.

The other way to safely inactivate the small remaining of copper in your tank is to make us of “chelating compounds”. You do not need to know anything related to the chemistry involved in this process nor do you need to buy anything extra. You can just use the normal water conditioner that you use for the removal of chlorine/chloramines. Many brands of water conditioners contain chelating compounds that make heavy metals (including copper) safe. Make sure that the one you are using does in fact contain some chelating agents and, since it is safe for use in aquaria, you may want to overdose a little to inactivate most of the remaining copper. This will eventually be eliminated by the regular 20% weekly water changes.


If you have followed these guidelines closely, you will at this point have a stressed, yet working and snail free aquarium ecosystem. It will take some time for the system to recover completely, but given enough time, it will happen. You will, at this point, have successfully treated a snail infestation with copper ions.

I just want to add one last word before finishing this article: As you may already know, “Prevention Is The Best Medicine”. Always carefully wash and disinfect all the plants that come into your aquarium and never let water from any fish store find its way into your tank. You and your fish will then enjoy a healthy environment that is nice to look at and safe to live in.