That is a Eurobrace .... it is there to prevent the glass from bowing out under water pressure. <And it does not have to extend from end to end to do the job ...> N. American tanks tend to have wide plastic stripe on the top trim frame for the same purpose.
At 18" the brace is prob. not that necessary ... you normally only brace long tanks like 36" or 48" & over .... but do check with the manufacturer, as they might use thinner glass in the panes & add a brace to compensate.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.