always use something that you can add circulation to standing water will stagnate so you have to have movment in the water for it to stay good I also suggest a heater to keep the temo stable before you use it. also let it have the ability to breath.
Mike
I Agree, keep water moving or you will wind up with film algea on everything. You can keep it mostly covered to keep dust and bugs out of it then it should be fine, but keep the water moving.
Thomas