I feed my big eel 24"+ usually every 2-3 days as much as she'll eat in a sitting (3-5 worms) my babies eat live blackworms and get free choice to eat as I keep the tank stocked with them 24/7 and dump 1/4lb in the tank once a week or whenever the sand looks empty ( one's a 10" fire eel the other a 12" starry night) I started them on nightcrawler 1/4s but sometimes its hard to get crawlers so I save them for the big girl and get the blackworms.
I found the majority of species after 2yrs or around there will slow down growth considerably, up until that point I feed often and as much as they will eat in a sitting fasting periodically. imo bloodworms and brine shrimp aren't nutritional enough to make up the bulk of a spineys diet and live blackworms,nightcrawlers, or other quality seafoods should be offered instead.
for small eels like your baby fire. freeze some tilapia ect and take a cheese grater to it. this works great for other fillet/shrimp/scallops ect.
some people also have luck with smaller red worms ect. so like Ben suggested.... try a variety of foods until you find some things they like.