I have a tank that is now over 15 years old. I haven't added any new fish in the past 5 years or so, knowing that I was going to redo my system. So that time has now come. I redid my plumbing, making use of my 15 years of experience to create a better, easier to maintain setup. Before I start to restock, I still have some old brittle stars, but everything else is gone, I am thinking to replace my sand bed. For an aggressive fish tank, where sand is only there for looks, what type of sand and what depth would be recommended? Thanks in advance for any replies, it's greatly appreciated.