Certainly an interesting mix of inmates there.
Unfortunately the barb and tetras will become meals very shortly.
The biggest thing to watch for is any gaps in the lid. Whilst eels are great escape artists, so are arowana, often ending up on the floor from an open lid or even a gap.
Most arowana will be on the lookout for items of food falling into the water and many can be trained to come take food out of your fingers, which still freaks me out every time he jumps to take it.
This means a little splashing and you can get their attention to give food items such as bits of fish, mealworms, crickets, etc. Personally not fond of bugs so mine gets mussels, fish and worms.