American Eel habitat
I have a small (~4 inch) eel in my 30-gallon tank. The tank has a gravel substrate with some plants. The plants have a small amount of soil around the roots of each one.
The eel likes to stay burrowed in the gravel during the day. It only comes out at night or when it smells food in the water. I've had it about a month, but for the first two weeks I saw it maybe once while it was adjusting to the new surroundings. This past week I've noticed that it has a red spot on the top of its head. It doesn't hold still long enough for close inspection, but I think it's a bloody spot. Could this be from scraping its head on the rough gravel? It's aragonite, crushed shells mostly. I've noticed that the eel prefers to burrow into the softer spot near the roots of one of the plants. I don't know if it's just established a burrow in that spot or if it's seeking a softer material.
I'm fairly certain it's not getting attacked by tankmates. The only other carnivorous fish in the tank is a 1-inch hogchoker sole that is also completely inactive by day, and doesn't burrow at all. I have provided an area of sand for this fish, but I've never seen it rest there.
Have I provided this guy a proper tank bottom?