Two Little Fishies MetaSorb UHC, 500-800 Gallon Capacity, is the solution for the excess of toxic heavy metals in your aquarium water. These toxic metals may come from the water source, from foods, from artificial seawater mixes, corroding metal equipment, magnets, pumps, etc. Sudden mysterious ailments in fishes, corals and other invertebrates may occur when heavy metals reach a toxic threshold.