I've got my jar in a barebottom , used to have gravel but lost it to keep ammonia and waste down in my tank , also much easyer to do weekly wc and helps my filters deal with the waste
I used to have sand substrate but I took it out and now bare bottom with a just a few rocks and pebbles. As what azura stated, it is a lot easier to maintain. My aro is a silver.
I have barebottom tanks one is painted black the other has a sheet of black acrylic on the bottom. 2 jardini and one leichardti . So much easier to maintain. I never have to gravel siphon just squeegee the bottom once a month or so to remove algae
My black aro is in a grow out that is bare bottom. Being top dwellers I don't think the aros care much what is on the bottom of the tank. Once he's a little larger he will go in my main tank that has sand. The sand is for the rays but there really isn't any maintenance with it and it looks nice.