the flow is an issue, might work for a five gallon or smaller but not much else as far being air powered, though as a vegetative filter box the flow rate might be good as well. the biggest fault was the noise, it made a sucking sound i couldn't fix! I'm going to hook it up to a small power head for the fun of it and see how that works. Yes it is a refugium, which as i understand it in a reef concept is used to safely breed edibles for the main tank, be a safe haven for new/weak/young/and otherwise sensitive inhabitants, as well as hide equipment and provide space for more complex filtration methods. All of which are important for freshwater tanks, plants or otherwise. a plant that might be delicate or invasive in the main tank but is a heavy feeder could be more easily contained in the refuge. or floating plants the would quickly blanket the water's surface. Algae could be grown in the refuge for the feeding of fish, or allowed to run rampant with in the space, thereby filtering while the main tank can be made algae free, though i fully realize that in a healthy planted tank the plants eventually out compete the algae no matter where it is. New born fry can surely hide in a planted tank, but can they compete with an adult sailfin mollie for food? there are also freshwater copes that could be raised or easily bred shrimp in the refuge. technically, almost all fish are predators to a degree, so yes our tanks are filled with predators. i just thought it would be nice to have a freshwater filter that could be run off of an air compressor and be adaptive.