The common Aiptasia Eating Filefish (Acreichthys tomentosus) - aka the Bristle-tail Filefish - gets about 3.5 inches (12cm). And a 30 to 40 gallon tank is recommended for them on various sites as the minimum size. So should be good. Just avoid more aggressive tank mates, as these guys from everything I have seen tend to be really peaceful, to outright shy and skittish.I like the wrasse but don’t filefish get huge?