We have been requested to investigate a sand filter for a 500GPD RO system. Near coastal FL still loads up the standard skinny cartridge 30m pre-filters. I was about to install a Big Blue cartridge filter until this request came in. Been dragging my feet but this week, I have to present a plan. Any sand filter users out there? Anybody thought about this? Oh also, under a cockpit deck, Max vertical is 34"