Well, I used crushed coral. The fish moved it around quite a bit. In fact, the tink tink tink of them spitting it onto the glass everymorning is usually what woke me up. The crushed coral will help to buffer your water, and one of the best reasons to use it, IMO. The coral sand, if that is what you want to use would work just as well in my opinion. They are going to move whatever you put in there, believe me. They make huge mounds of it against the glass. I don't know about it being more natural to them, as there isn't any coral in the rift lakes. There are shells however, which when they break down look about the same as coral sand.
If you don't need the buffering of the coral, you could just use regular pebbles, but I wouldn't use the gravel from the fish store that is colored by an epoxy on the outside. I found that it wears off really easily and makes a horrible mess. Just go get some river pebbles from a local landscaping place, making sure you rinse it really well in dechlorinated water. It will not only look a ton better and more natural, but it will cost you a lot less in the long run as well.
The fact that they move so much of the bottom material though means that you have to be very careful about your rock work. A tip someone told me when I started my tank was that before you set the tank up, spread a layer of aquarium sealant (100% pure silicone, no additives) on the bottom of the tank. Then pull a comb or fork through it so that it makes little ridges. This will make a cushion on the bottom of your tank so that if the cichlids remove all the bottom material from beneath the rockwork, it won't be as likely to crack from the weight of all the rock resting on bare glass. Believe me, this one little step will save you tons of worry. You still want to be careful stacking rock though, make it as stable as possible so that there is little chance it will fall into one of the side panes if the do remove the gravel from underneath it. I never had it happen, but I worried about it.
Man, was this long enough or what, LOL?
Jan
