Please be consider that MACHITE GREEN has very danger side effects in Fish and human and its mutagen, carcinogen and teratogenic effects were approved many years ago so avoid from using in your aquaculture farming,

Which does the symptom is exhibited by fish ? Based on the symptoms, we can use the chemicals. Any how FMC is more over better in fish disease. But,  the concentration is very much important. The fish will be affected, if the concentration is exceeds. Yes. off-course, all the chemicals are having side effects to the fishes. 

You can use Copper sulphate singly at very low levels say 1 to 4 ppm & that too for very short periods of time for diseased fish immersion,which again depends upon type of disease & body weight.

Dear colleagues,

Please avoid from using of MALACHITE GREEN in your hatchery and aquaculture farms. This chemical mater seems very danger not only for fish and aquaculture but also for human societies.

Also, It's a known carcinogen for humans and can be lethal to fish.

Please pay attention to some documents as follows:

Toxicological effects of malachite green:

http://www.ncbi.nlm.nih.gov/pubmed/15129773

Negative effects of malachite green and possibilities of its replacement in the treatment of fish eggs and fish: a review

http://vri.cz/docs/vetmed/52-12-527.pdf

Toxicological effects of malachite green

www.vliz.be/imisdocs/publications/55669.pdf

Maybe we like our fish and environment globally.

Using CuSO4 you treat not only parasites but also kill algae.It results in droping the level of oxygen in your pond because CuSO4 is toxic to algae.It is more toxic in water of low alcalinity than in water of high one.CuSO4 can be also toxic to fish .And some fish are more susceptable than other.So before using a new treatment you have to check susceptability of several fish in small aquarium with water from your pond.

Both of the formulations suggested are very old. Formalin and methylene blue mixture was a standard method for killing white spot ( ichthyophthirius) up to about 1970, and Malachite green is an excellent treatment for fungus infections. Malachite green is still sold legally in Australasia for treating ornamental fish (pet fish), but as other posters have said, is a carcinogen and has been banned from all food fish use. The EU have very strict testing for malachite green residues.

Copper sulphate is sometimes used as a treatment but, as has been mentioned, it is lethal to algae and aquatic snails and the LD50 for many fish species is very close to the effective dose, so it is not uncommon to kill the fish by mistake.

For advice on chemicals licenced for use in Australia, together with the dose, methods of use and precautions (including withholding periods), see the Australian APVMA website at http://permits.apvma.gov.au and search on "fish" with "animal/crop" highlighted.

formalin, for example, is at http://permits.apvma.gov.au/PER14489.PDF

you can use copper sulphate in small mount in case of individual treatment of infected fish in aquarium.

Application of copper is effective in selected situations.  I an not sure which disease you are refering to, but copper is very effective on water molds (fungus) and columnaris and has been effective on parasites like icthyobodo.  Do a literature search on Dave Straus.  He and his lab have been turning out some good information on copper.  Please mind you water quality and low alkalinity and copper do not work well to gether.

Although MACHITE GREEN is very toxic effects in Fish and human it is very effective for fungus and algae. But you can use formalin for treatment of fish also..

I believe that  mutagen, carcinogen and teratogenic effects of MALACHITE GREEN would be more than treatment effects in fungus and algae. Please consider its fetal and permanent effects in environment. Please think to future generation and avoid from chemical components in your aquarium or fish farms.

I invite all of you to using some useful herbal medicine as my country that we can try to finding suitable alternates such as Zataria multiflora.

In IRAN we approved some herbal extract instead of malachite green , for example we used from zataria multiflora extract for incubation period of trout as a fungiside and antibacterial drug . please follow my article in research gate.

against piscinoodinium (particularly)

saprolegniosis

snail

monogenes

dosage:0.1-0.2gr/1000lit in hard water or 0.05-0.1 gr/1000lit in soft water.

There is an Australian  Minor Use Permit for the use of Copper sulphate to control fish parasites The pdf can be found at the link below.

Note in particular the caution: The toxicity of copper sulfate on fish varies with temperature, exposure time, concentration and fish size. Other factors to consider are fish species, stocking density, water quality, production stage, parasite species and levels of infestation. The algaecidal effects of copper sulfate will lead to the death and decay of phytoplankton which will lead to a significant reduction in water dissolved oxygen levels. The resultant increase in ammonia and nitrite levels could also adversely affect the fish. Pond water alkalinity will need to exceed 50 mg/L CaCO3 to remove any possibility of toxicity to fish. These factors also affect the efficacy of any treatment protocols. 

http://permits.apvma.gov.au/PER14748.PDF

how make anti alga for ornamental fish tank