I would think if you can afford an indoor arena that you can afford a good arena grooming tool (there are several good ones) and the right dirt on the floor.
I think this is a case where they deliberately spent more money to get what they thought was the best material, but in the end turned out not to be. Would have been a lot better off and cheaper with the right kind of soil. They're spending lots of money to do things right, this just turns out to be a bad choice.