Since I don't use antibiotic anymore (due to harshness to both the fish and environment)...I can't say much about their use, however, once you start them you need to complete the course so not to cause resistant issues
I would monitor the ammonia as you are doing and make water changes as needed based on the results and just use that medication as directed on the label and if it is ineffective once the course is completed then I would start the Epsom salt treatment at that point
Its always best to QT with any type of treatment you use especially in cycled tanks and with live plants as well as for observation purposes....antibiotics can't tell the difference between the good and bad pathogens and kills them all and some live plants can be sensitive to some medications and sodium chloride (aquarium salt)-low does of Epsom salt (magnesium sulfate) are usually tolerated/used as food by live plants but high doses needed for treatment can sometimes be harmful.