I don't know what the back compartments contain, exactly, or if they already contain these things, but you could run carbon and/or a phosphate remover/binder (rowaphos, phosban, phosar, etc.). I know some others also place live rock rubble in the back compartments, but I would be afraid of detritus build-up, personally.
Could you convert it into a mini refugium? Get some chaeto and a light? Just rambling
