I have never run a refugarium but it would seem to be similar to the plant tubs I have used for smaller fw ponds, I used a poly watering troughs that had the filter outflow pumped to it's bottom so that the water flowed up through a thick layer of pottery shards and around potted cattaails or pygmy japanese lotus and a bunch of floating plants (usually water hyacinth but sometimes water lettuce). I would throw in killies, gambusia, or guppies for mosquito control and fairy shrimp and crayfish as well, they bred enough to make a source of occasional fish snacks. This set up was gravity fed through a screened tray back into the pond over a splash tray. It seems that continuos lighting would cause an algae bloom.