I previously had a 230L on an Indian piece of furniture. The top surface was really uneven.
I added a layer of about 12mm foam board and on top of that a chipboard. Leveled everything with wedges. Worked like a charm. I made a trim to hide the foam and chipboard. Not sure if that's for you, but you definitely don't want 200L of water on the floor. If it's full glass, it needs to be even underneath...
I believe an aquarium weighs more than 1kg/L. Yours will probably weigh over 300kg once you've added gravel and stones.