I'd lay off the brine completely unless it's all they'll eat because it's not very nutritious. Bloodworms are moreso, but mainly just a source of protein. Try and mix it up with glassworms (mosquito larva), small chopped up earthworm, tiny chopped beef liver (good for growth in juvenile fish), chopped mussel/clam (usually available in frozen section), amphipods/scuds/gammarus (buy freeze dried, frozen, or buy/breed your own - really easy to get a colony going), and they may also take chopped up raw cocktail shrimp, fish filet, and crawfish meat.
I also feed my small fish small live water insects. If you set a bucket of dechlorinated water outside with a little bit of fish flake you'd be surprised what shows up. You can even feed any moquito larva (check daily so you don't actually start propagating mosquitos in your yard
). And make sure to avoid larger predatory water bugs.
A good variety goes a long way to healthy fish.
And of course try to get those nitrates down. With all the feeding baby eels need it's important to siphon your substrate and rinse out your filters often, and do water changes as often as possible.
