Unless you have bright fish like Albinos and/or certain Cichlids, black on black will make them fade into the darkness. I have black sand and had a black backgound. I found that it was hard to see the fish, unless they had some nice color on them. My Jag, RCK, CK, Dats, and Chinese Perch would blend into the darkness. My Albino Oscar, ACK, GT looked great in there. Just something to think about when picking your stock.