TRUVU Refugium Filter. Photo from TRUVU.
Refugium filters are common in the marine hobby, but are often overlooked by freshwater aquarists. A refugium, by aquarium hobby definition, is a container that a refuge for ecosystem organisms. A refugium is typically an aquarium placed underneath the main display tank that has water cycle through it from the main display. Most often it houses fast growing plants that help remove nitrate from the aquarium system. Refugiums primary purpose is to remove nitrate, but it can also be used to harbor small shrimp or fish that would otherwise be eaten by fish in the main display. Refugiums are usually brightly lit with CFL, High Output T5, or metal halide lights to stimulate vigorous plant growth, and uptake of nutrients.
A refugium filter should be considered if you plan on keeping fish that are not compatible with aquatic plants. Large Central and South American cichlids like, oscars (Astronotus ocellatus), peacock bass (Cichla ocellaris), red devils (Amphilophus citrinellum), and others can all benefit from the nitrate reduction capabilities of a refugium.
Hydroponics filtration is a very effective way of removing nitrate from the aquarium system. Many types of plants can be used with a hydroponics filtration system, including edible plants. Hydroponics systems are more efficient at removing nitrate from the water than plants submerged in the aquarium because of the higher concentration of carbon dioxide in the air. A hydroponics filter can be placed either above or below a main display.
Hydroponics systems should also be considered for fish hatcheries to optimize water quality and fish growth rates. Large aquariums with fish that would normally eat or damage aquatic plants are prime candidates for a hydroponics filtration system. A hydroponics system can also be used as container for a breeding colony of freshwater shrimp or small fish.