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Copper sulphate as a fish disease treatment

Copper sulphate (sulfate) can be used to treat a range of parasites affecting marine aquarium fish. Protozoan parasites such as Crytocaryon  (marine Ich), Trichodina, Amyloodium  (marine velvet disease) as well as monogenean flukes – Dactylogyrus  (gill flukes) and Gyrodactylus (skin fluke). It is not recommended for treating freshwater fish.

Using copper

Copper is active against many marine protozoan and monogenean parasites, but its use can be complicated. Copper is easily de-activated because it reacts with calcareous material often found in marine aquariums, i.e. coral and limestone, to form insoluble copper carbonate.

The solubility of copper is highly dependent on pH. As pH increases above 7, copper precipitates out of solution – 100x increase for every one-unit increase in pH. The danger is that should the pH of the tank drop, that is become more acidic, then the level of ‘free’ copper can quickly rise to toxic levels as the precipitated copper is re-dissolved. In addition, organic matter also binds up copper.

When treating parasite disease, the free copper level must be maintained between 0.15 - 0.20 mg/litre. If the concentration drops below this range it will not kill the parasites. If it rises above this level then it will kill the fish! Copper will also adversely affect invertebrates. Because of these complications it is advised never to treat the community tank but instead treat affected fish in a separate hospital tank.


A stock solution is prepared using 1 gram of copper sulphate (CuSO4.5H2O) to 250 mls distilled water. This solution now contains 1 mg copper per millilitre. The initial dose is 0.15 mg copper per litre. Therefore if the tank contains say 200 litres then the dose required will be 200 x 0.15 mgs copper = 30 grams = 30 mls of stock solution.

The copper level of the tank should be measured immediately and thereafter twice daily using a test-kit that measures in increments of at least 0.05 mg/litre. If the residual copper level in the tank drops below 0.15 mg/litre - then add additional doses of 0/05 mg/ litre of the stock solution until the optimum level is restored. Using the same example 200 x 0.05 mgs copper = 10 mgs copper = 10 mls stock solution

Copper can easily be removed by activated carbon

Useful conversions are:

ppm = mg/litre            i.e.  5 ppm = 5 mg / litre

mg / litre  x 3.785 = mg / gall (US)           i.e  5 mg / litre = 18.9 mg / gall (US)

mg/ litre x 4.546 = mg / gall (UK)            i.e  5 mg / litre = 22.7 mg / gall (UK)

To convert imperial gallons to US gallons multiply by 1.2


Other useful figures: 

1 ounce = 28.35 grams


1% solution = 

10 ml per litre

10 gram per litre

38 gram per gall  (US) 

45 gram per gall (UK)   

Fish disease problems? Need some help? The help pages take you through the basics of the 'fish health work-up' diagnosis method and basic fish disease treatment methods.

90% of all health problems and fish deaths are caused by poor fish keeping! The key pages are essential reading for all beginners and intermediates who are serious about disease prevention.

Expanded Content by Dr. Erik Johnson, and Used with Permission; Frank Prince-Iles ©2009 All Rights Reserved