Very nice setup. The MH really enhance the look of the tank.
Do you have ball valves on your plumbing? For maintanence or emergencies, etc. You can also create a little back pressure with a ball valve and get rid of the gurgling and toilet flush noise from the overflow pipes.
I was planning on getting 3M black S grade sand, but couldn't really find it anywhere near me. Not without paying more for shipping than the sand.
I ended up finding a product called Estes Medium Broadcast. It is pretty much the equivalent to 3m S grade. The Estes Medium Broadcast is used for painted or epoxy floor applications. You can find it at any paint wholesaler and probably some retail locations. There are about 15-20 colors to choose from. I found it locally for $0.48 a lb.
Here is a pic of it in my tank. You can really see the grain on the disc of the ray. Each grain is really round and smooth.