I agree with aussie, even a few plastic plants would give it more natural character, and you wouldn't have to worry about specific lighting.28 l tanks look better to add View attachment 448061
They asked for aquascaping options, not stocking options. So didn't bother mentioning.I am really surprised that nobody noticed the fish you have in there.
You said the tank was 28 liters? If you have that small of a tank, and there’s a bala shark in there, you have problems.
Bala Sharks get up to a foot long, or bigger, and will require a larger tank, minimum of 100 gallons, with larger being highly recommended. The black skirt tetras are fine.