You might want to read the comments that I posted today in the following discussion.
http://monsterfishkeepers.com/forums/threads/treating-a-small-fish-for-hex.651285/
Adding Epsom salt to the tank water may help flush the parasites, but it will not cause them to die unless ingested directly into the gut. Metro on the other hand can cause death via a bath. I explained how this works and posted link to a 200+ page study that explains some pretty detailed info on this disease.
IME Hex-Shield must be nasty tasting stuff, but if your fish will eat it, feed for 3-4 days straight and it should nuke any Spironucleus vortens aka Hexamita parasites. My fish all ate the food (in a comm tank) but they weren't exactly fighting over it like they usually do, and after a few days some of them started to refuse it. Good news is it worked to perfection, and cured a pretty serious problem. Make sure that ALL fish in the tank are eating it, and offer no other food during this period. Metronidazole should not be used for two weeks straight, but I understand your desperation and why you dosed that long. As far as cost, save the metro for down the road - not much point in saving a fish only to have it later die from organ failure from over medicating.
Sometimes no matter what we do these things cannot be beat, and of course short of a proper identification by an expert in fish pathogens and protozoa we are generally just making educated guesses.
Edited to add a repost from a past discussion on this topic .....
A few things to note when treating with metronidazole, it has been found to cause organ damage in fish if used excessively.
Metro applied via feed should only be done based on the fishes weight.
Dr. Edward J Noga suggests
1. Bath
a. Add 19mg/gallon and treat for 3 hours. Repeat every other day for 3 treatments.
2. Prolonged Immersion
a. Add 25mg/gallon and treat once daily for a total of 3 times.
b. Add 95mg/gallon and treat every other day for three days.
3. via feed
25 mg/Kg of body weight/day for 5 to 10 days, or 100 mg/kg of body weight for 3 days. Retreat once if required.
Dr. Edward J. Noga, MS, DVM, is a highly respected professor of aquatic medicine and immunology, that has been published approx 150 times in related papers/journals. His lab at NC State University specializes in the study of infectious diseases of finfish and shellfish. His book, Fish Disease: Diagnosis and Treatment is the go to "health" book for every serious fish keeper and aquatuc DVM on the planet.
Good Luck!