Used as a redox indicator in analytical chemistry, Methylene Blue Trihydrate helps detect oxidation-reduction reactions, changing color based on the solution's redox state. It serves as a biological stain in microscopy, enhancing visibility of cells and tissues under the microscope. Commonly applied in medical diagnostics, it aids in identifying abnormal cells during surgical procedures. It is also used in aquaculture and fishkeeping to treat fungal infections and parasitic infestations in fish. In some cases, it acts as an antidote for methemoglobinemia, helping restore normal oxygen transport in the blood. Additionally, it has been explored in photodynamic therapy for its ability to generate reactive oxygen species when exposed to light.