If you want a quick way to see if your aquarium is bowing out, or to what degree it is bowing, all you’ll need is a piece of string. Simply put one end of the string on the front right corner of the tank and run it along the pane of glass to the opposite side. If the pane of glass or acrylic is bowing, it will not line up with the string. This simple trick can be applied to all sides of an aquarium, but it will only show you if there is any bowing. If the bowing is only slight, a relative term I know, then the structural integrity of the aquarium should still be fine. However, if the bowing is more severe, you might need to take some corrective action to keep a seam from splitting or some other failure of the tank. These corrective actions include draining the aquarium and adding bracing to the top or bottom, or possibly tearing down the tank entirely to use thicker glass or acrylic.