Adding extra garlic to food will sometimes encourage a picky eater to eat more, but it sounds like you may have something more serious taking place. Also, garlic will have no effect on the epsom salt, so no worries there. Force feeding the solution is the same as presoaking the food, it should be done for 3-5 days.
For more serious cases, where the cause of the ailment is unknown, or the fish appears to be on its way out, treating with Clout is another option.