Welcome to AA!
Are these tanks you already have? The 14 and 55, that is. I'm not convinced you can't do better with just the 55 sectioned off. Its not like you're gonna get much lr
in the 14 to make it worthwhile I'm thinking. If you did do it like that, I'd think the rock first for the return from the main where its more crashing return stuff going on. Then, easily flow into the quiet, slow area at the fuge.