I have used the product Quick Cure more times than I would care for. It is formalin,Malachite green.Should be used at half dose for sensitive or small fish and though the product says it can cure Ich in two days, I would treat for seven days minimum.
When I had occasion to use it, I treated the tank daily for three days. On fourth day,, I performed 25 to 30 percent water change and then treated tank for another three consecutive days. On fourth day, I performed 25 to 3o percent water change and observed the fish after that for a week. If fish showed no more signs of parasite, I simply put medication away. If fish still exhibit signs of Ich, then repeat steps as before. Always remove carbon if carbon is used for it will remove the meds making them ineffective.