What type of gravel are you using, is it pet store brand bought just for the color? And how attached is your son to it? It is possible to clean everything for reuse, but it might be easier to dump it all and start fresh if you're already that close. If you're like me then the first setup was by how the kids wanted it, but it might be worth steering them in a different direction as you learn more and what would be healthier for the stock.