You should specifically avoid copper, Potassium permanganate and Formalin.
Copper: This is can kill algae, bacteria, and parasites, but it is also very toxic to snails and other invertebrates. It accumulates in the water and the snails’ bodies and cause irreversible damage.
Potassium permanganate: This is a chemical that can oxidize organic matter and pathogens, but harms snails and other beneficial organisms. It can burn the snails’ skin and gills and cause stress and death.
Formalin: This is a solution of formaldehyde that can treat fungal and parasitic infections, but it can also irritate snails and other aquatic life. It lowers the oxygen levels in the water, causing respiratory problems.
Consider these instead:
Malachite green can be used as an antifungal and antiparasitic agent to treat fungal infections, ich, velvet, and other external parasites. It is usually added to the water as a liquid or powder, but use half the recommended dose for snails and monitor the water quality closely.
Praziquantel can treat internal parasites such as tapeworms, flukes, and nematodes. You can use the normal dose with snails, just change the water after the treatment is completed.
Kanamycin can be used to treat bacterial infections such as fin rot, dropsy, and septicemia. It is usually available as a powder or granule. You should use the normal dose for and perform a partial water change every day.
