The first thing is do not panic too much over this. Eels can be very picky at times, and you need to remember they can go a long time without eating and still be fine. I have a huge moray I've owned for five years, and he has gone through periods where he just won't eat for months, and I mean two or three. He has gone through two of these "hunger strikes" in those years, and both times every parameter of the tank was fine and there was nothing amiss. Then of all the sudden, he started eating daily again w/ no sign of problems. So that's my first suggestion, don't panic, it's not going to kill your eel if he doesnt eat for a few days or weeks.
Sometimes an eel will not eat due to changing stages in life. As my brackish eels matured, they stopped eating until I upped the SG in their tank. As marine eels mature, their needs change sometimes as well, only not in terms of SG but rather diet. As marine eels progress through stages of life, and sometimes move into deeper regions or furter to open sea, their diets may shift. Some marine eels I have had tended to exhibit the need for a different diet as they matured. My SFE is not old enough yet or hasn't hit that barrier yet, so not sure how responsive yours would be to feeding cycles.
But in the meantime, see if a different food while initiate a feeding response. Try krill, silversides, ghost shrimp, fresh pieces of shrimp, fresh squid, fresh white fish, and try introducing a garlic additive on the fish or directly into the water (check a local fish store if you want straight-out-of-the-bottle garlic additives).