I realize that I am not the expert on saltwater tanks, but have one like you that I just begun a few months ago. I wanted to chime in on the crushed coral subject because from this forum and the advice that I read about CC, I actually took at better look into my 55 gallon freshwater tank and the gravel substrate I have had in there for nearly a year now. I wanted to point this out because I was foolish and kept adding more and more gravel in the first month or so of having my 55 gallon tank (my first tank, by the way) because I had put all black gravel in it and then wanted to add color to it. Eventually, after adding some blues and greens, I ended up with a 3 inch substrate layer in the tank and like you point out, had planned to keep vaccuming it out with water changes.
I feel this is relavent to a SW tank, because from my observations, four inches of substrate is usually the recommended layer for a SW system. (Because of the bigger need for more bacteria in most cases, but humor me a bit here) So, the other day, when looking at my 3 inches of substrate, that I religously vaccumed out, this is what I was able to 'kick up' into the water:
This is a picture of my tank from looking down on the top. You can clearly see how 'muddy' it looks and from this angle, the water is clear compared to what it looked like at the bottom. Needless to say, I changed to sand that day and realized the ideas and info that are being pointed out about CC are not just someone's opinion, but an informed opinon.
I just wanted to share that with you because while I am not an expert by no means, I am not brand new to the hobby and I promise you that I did not neglect my tank at all, this waste and detrius just built up without me knowing it. I really think that your tank is amazing and would hate to see you have problems a year from now (or even earlier) because you thought you were doing everything right, like I did.
Like I said, amazing tank though. I really love it and it is a good example of a tank without using tons of live rock. While I have seen quite a few tanks without live rock in person, I do not usually see people on forums like this one going that route.
. I love the simplicity of it all.