Given the immense popularity of refugia in the marine aquarium hobby, you might be left wondering if they work in freshwater systems. While they haven’t quite caught on yet on the freshwater side of things, they are just as applicable.

Freshwater refugia do indeed serve the same purpose: Remove excess nutrients from the water (thereby reducing unwanted algae growth) and support large populations of small crustaceans (copepods, amphipods, ostracods, etc.). If there is any real difference at all, it is in the type of “plant” used. Marine refugia rely principally on macroalgae whereas freshwater refugia use mainly true plants.

There are so many aquatic plants available that it is surprising that freshwater refugia aren’t more widely used than their saltwater counterparts. Some types, though, are better than others. Slow growers such as Cryptocoryne, for example, might not be the best choice. Big, leafy, self-shading varieties like Anubias aren’t so great either. Mosses, worts and other tiny types of plant are just too messy and difficult to contain properly.

Better types include tall, fast-growing, deeply/densely rooting types that don’t mind living in thick clusters. These are regularly harvested in sections (either clipped back or pulled at the root) to allow for continuous growth. Thus, plants like Vallisneria, Stuckenia and Elodea work spectacularly.

Now, just because a plant could work well in refugia doesn’t necessarily mean that it will. For the high growth rates, you’d want in a refugium, you must provide very intense lighting to support optimal photosynthesis. A mineral-rich substrate can’t hurt, either!

Refugia are suitable for all types of freshwater systems. Though it might seem counter-intuitive, they work really well on planted systems. Why? Partly because they provide a huge, regular supply of pods, which keep the leaves of plants in both tanks (main and refugium) clear of detritus and fouling algae (fish in the main tank would eat all the pods without a refugium!). Also, when maintained on a reverse light cycle, a planted refugium helps to maintain a stable pH throughout the whole system, day and night! For sure, refugia are destined to gain acceptance among both beginning and advanced freshwater hobbyists.tr