I've used gravel substrate (the small pebbles from a landscaping store), a type of holely rock and with a UG filter and crushed coral in the canister filter. It was a7.5 gallon cube. Used salty shrimp 7.5 and RO water at first. Got tired of doing that and used tap for water changes (monthly). There were about 4 orange rabbit snails in there. My cardinals did great until I moved then the colony crashed. The rabbit snails were placed in a junk tank (20 gallon long) with some gravel and hob filter. Another 4 snails were added and 2 years later when I broke it down and moved the snails I found about 40. The picture is the new tank with the snails