When you say the "brace on the right hand side" I assume you are talking about the 1 inch horizontal piece of glass on the right? (the tank itself will always be the same level based on the height of the overflow.) In other words, you can't control the water level in the main tank, the overflow isn't adjustable.
The manufacturers recommended water level in the BACK is represented by the plastic bar on the sump viewing windows on either side of the sump on the outside of the tank.