that is a good sized tank for him
many people say for snowflakes, that if it will fit in his mouth, he will eat it. But this depends entirely on the eel itself. They are invert eaters by nature, but some have been known to snack on a fish. Some will not even eat your shrimp, hermits, ect. The best way to make sure that he wont, is to expose him to them while he is younge. Then he will no longer think of everything there to be a food item. What fish do you have that you are worried about him eating?>