Have you cleaned the impeller/tube/tub portion of the HOB at all, Greg? I know some people are lucky with their water and I don't know what yours is like. But mine leaves a scum/goop on everything and eventually it starts coming off in small pieces.
Additionally, my gravel tanks just always look like this. I know you said yours used to be clear, but my gravel tanks just have... stuff... floating in them. I tore the last one down this weekend and put it on sand. And immediately it's crystal clear. Not 100% sure why necessarily.