It was active a couple hours yesterday up until I fed it. (I was trying to feed it sooner but Petsmart decided to take forever to tell me I couldn't have their ghost shrimp because "they need a couple days to acclimate to our tanks before we can see them".) But so far its schedule during the day is a few hours of nothing followed by 5-10 minutes of swimming/foraging on the sand, repeat. But at night it is very active.
I'm looking at a bigger tank but I do have weight and money restrictions but I'm hoping to get something within a couple months. I'm looking at a 90 gallon right now or a larger acrylic. That would be when I'd look more into substrate too. I'm thinking I look at garden eel care guides for substrate suggestions?
I'm also thinking about tank mates once I upgrade. My LFS kept it with several other eels, ribbons, snowflakes, and another BSE, and never had any problems. He suggested a zebra eel as being the best eel due to its lack of aggression. His other suggestions was one of the more peaceful pufferfish.
I know these could just be sacrificial offerings, but I'm extremely curious to know how it does with small peaceful fish. The videos of them online make me think they might be disinclined to pounce on a fish mid water column unless very hungry.
I'd love to see how they did with a salt acclimated freshwater molly added to the tank as a trial. A Molly would have the benefit of not being a potential disease vector, and is captive bred and cheap, so if it becomes a snack, it's ok.
Personally I would not be inclined to make this a traditional predator tank. The eel is pretty derpy and a puffer could do some serious damage. Maybe.
I'm sure it will be fine in the smaller tank for now as long as you keep up with the water chemistry and don't add a whole ton of other fish.