With turtles it's more than just putting one into the tank. You'll need to provide a basking area, they need to dry off and warm up. You'll need to provide a UVB source.(expensive light bulbs) then heavy filtration, rated twice that of the fish tank. like for a 60 gallon tank, you need one that'll handle 120. Turtles are poopy messy little stinkers. Proper food in the form of pellets, fresh foods including live worms. I prefer two together, some keepers claim turtles do not like companions- mine do. If you look at Red Ear sliders, don't get a girl-they get HUGE. A male can live well in a 75 gallon minimum size tank. Map turtles being smaller you can get away with a 60 gallon.
Gravel is not recommended for the bottom of the tank, turtles can ingest and get blocked up by it. Larger river stones are best if you want something on the bottom. It's just has to be bigger than their mouth. Any decor is up to you. Many keepers forgo the stones on the bottom keeping a boring bare bottom tank but it's said to be easier with cleanup.
Who said turtles don't need height? Pond turtles should not be touching the floor in their tanks! They should swim freely, tall wide and long tanks are ideal but the ultimate is a pond.
