I just got a 55 gallon tank, and I have a few questions about setting up the tank for cichlids(african, but I haven't decided on what types yet) I've read they like sand, does it matter what kind? Can I get the white sand that is for kid's sandboxes as long as I rinse it well? Can/should I use the underground filter with sand? Or would it be better to use the regular fish tank gravel? Would it be better to put limestone rock or large river rock in it? (I have access to both) Would it be ok to put a some of my adult guppies in the tank to help cycle it before I get the cichlids ? (then remove them) I have 29, 20, and 2 gallon tanks going right now, but I've never had cichlids, and I wanted to make sure I set up their tank the way they want. Any help would GREATLY be appreciated! THANKS!