There are many products available at your local pet store that can help treat ich. Always follow the instructions labelled on the medication for the correct dosage amounts and if it's safe to use on your type of fish, especially if you have invertebrate fish such as snails, shrimp, and clams.  Always perform a water change and vacuum your gravel before you administer the medicine. Medicine is more effective in a clean tank without other dissolved organics or nitrates to get in the way. Always remove the carbon from your filter as the carbon can neutralize or entrap medicines added to the tank. Since saltwater ich lasts much longer in their tomite phase, copper is often added to the tank for 14 to 25 days and works similarly as salt to destroy ich. However, using copper requires you to put in the exact and correct dosage and diligently check copper levels in your tank daily with a copper ion test kit. Do not use copper to treat freshwater fish because it could kill them.  Always follow the instructions on the product. Remove the carbon from your filter as the carbon can neutralize or entrap medicines added to the tank. Copper combines with calcium carbonate or magnesium carbonate based rocks, sand, and gravel so be sure to only use copper in a bare tank. Copper is highly toxic for invertebrates, reefs, and plants. Separate invertebrates, reefs, and plants and treat them with other safe methods. These methods can be dubbed as dangerous alternatives to treating ich. Some even damage your fish and must be constantly monitored so levels don't reach to a point where your fish might die from the chemical. Always read the label of these chemical medicines and wear protective clothes like gloves and goggles when handling them. Some treatments are:   Malachite green: Similar to chemotherapy in humans, malachite green works to damage all cell's ability to produce energy which is vital for metabolic processes. This chemical doesn't differentiate from a fish's cell to the cell of an ich parasite.  Formalin: Formalin kills microorganisms by reacting with a cell's proteins and nucleic acids which alter the cell's function and structure and often used to preserve biological specimens. It can damage your filter system, deplete oxygen levels and kill invertebrates or weaker fish.

Summary:
Use medicine products to treat your tank. Use copper to treat saltwater fish with ich. Use stronger chemicals to treat saltwater ich.