first of all, you need to get some kind of lid for that bucket, otherwise you're going to find it on the floor. eels are notorious escape artists and will find a way to escape.
eel - saltwater or brackish (1/2 freshwater 1/2 saltwater, not freshwater with regular salt in it). under no circumstances should you be keeping the eel with angels as angels are complete freshwater and need no salt, unless there is an ich problem that you are treating. salt should be dissolved in a small container orf tank water, and then slowly added to the tank. putting salt in a cup and keeping the cup in the tank is something i have only seen in stores, so they don't have to mix salt every day. why do you have a cup of salt with the angels? completely unnecessary, and potentialy harmful to them over the long term.
why don't you just take the eel to a store that has a saltwater section and the ability to care for it properly? eventually it will need a fully marine (saltwater) tank, probably sooner rather than later. are you going to be able to do that?
is he still in the bucket or is he in a tank? are you using marine salt? otherwise it doesn't count as brackish. is there even a filter? eels eat fish, so they need to be kept with larger semi-aggressives.