Try not to feed them more than a few times a week at most. Every 2-3 days should be plenty. Each time you feed keep offering the eel food via feeding stick until it stops accepting it readily. They do have a limit but if fed daily, you will end up with very large water quality issues.
Also try varying the types of meaty fair. Krill, shrimp meat, scallops and other types will round out the eels nutrition. You can also try soaking the foods a vitamin every so often for added benefit. Just be sure it's not spurlina based, mine ignored that stuff.