I don't think that tilapia would do a very good job at absorbing the meds, I would also suspect that most would wash off upon hitting the water.
Keep in mind that unless one is looking at smears under a microscope, and knows exactly what to look for, it is near impossible for most hobbyists to be 100% certain as to what they are dealing with. What one thinks is Spironucleus could actually be a case of Crytobia iubilans, or even a severe bacterial infection. Also, Spironucleus is capable of becoming systemic, so if those parasites travel into the blood stream and settle in organs, chance of recovery becomes much more slim with each passing day.
Not sure about Metro, but magnesium sulfate will stay active once mixed with water indefinitely I would think. Weeks/months for sure.