Basic dechlorinator contains Sodium Thiosulphate to break down chlorine. However, it doesn’t break down chloramine.
Depending on what disease you want to treat will determine on what medication you make. Most common broad-spectrum medications contain formalin, methylene blue & malachite green. Formalin and malachite green are both carcinogenic (cause cancer) and should be handled with extreme care.
Copper sulphate can be used to treat whitespot.
Flubendazole/ flubenol will treat internal parasitic worms and skin and gill flukes.
I'm not sure on dose rates but some bottles will tell you percentage of chemicals per x amount of solution. Perhaps check the packages on some medications and take thew dose rates from that.