if you're thinking about african cichlids, they would prefer hard n alkaline water, both of which can be achieved with smashed coral sand as substrate. if you're thinking of dwarfs such as rams or apistos, they prefer soft and acidic water. you can decrease pH by using blackwater. shellies like conditions similar to africans and they're cool (yeah maybe i like them alot and am trying to psycho you to get some) hehe