i have a 55 gallon mixed cichlid tank and right now it is a bare bottom tank with river rocks that i have collected out of a local river. i want to re-scape it and need some help on what would work best for the bottom. i was wondering if i could have a clean up crew of cory's and oto's or are my cichlids too aggressive? anyways about the sand or gravel which is better? name of brands and places to get them please and thankyou!