Due to space issues in my dorm room, I've had to downgrade Octavius to a 1.5 gallon tank. Same with Hestia. However, they both love their little tanks. Hestia's tank has natural rocks at the bottom. As an experiment (and safety precaution), I decided to put sand in Octo's tank.
Surprise... surprise - he loves it! When I first moved him into his new tank, his sand was perfectly flat. Now, it looks like the bottom of the ocean. It has natural valleys and hills. Octo loves to dive into the sand, wriggle around, and then speed around the tank like a demon possessed. He's definitely thriving in his new tank too. His colors has been changing much, much faster than I expected a marble to, and his tail is turning bluer by the day.
Before, in his 3 gallon, I was worried that he was going to do some real damage to himself because he kept digging in his gravel (glass stones) and rubbing his entire body. He actually lost a few scales this way.
With the sand, Octo can go on as many rampages as he want, and he has less chances of hurting himself unless he gives himself a concussion.
So, long post short, if anyone's considering sand, I absolutely encourage you to get it! Best fish-related purchase I've ever done (other than getting the fish themselves).