An aquarium term, bio-load is the nitrogen processing demand placed upon the material, chemical and biological filters by uneaten food, decomposing inhabitants, accumulated organics and waste produced by livestock, foods and plant matter in the aquarium filtration system. This is not to be confused with bioburden, which is the number of microorganisms with which an object surface is contaminated.
Bio-load is determined by the net water volume of aquarium system (display tank, and sump), refugium, substrate, mechanical filtration, live rock, additional biological filtration, chemical filtration, chemical reactors, circulation, water changes, stage of nitrogen cycle, number (in short, the capacity) verus the size and number of fish, shrimp, crabs, snails, anemones, clams, other invertebrates, including filter feeders (in short, the biological demand). 
Aquarium filters remove, reduce and break down the bio-load. Biological filters include deep sand beds, wet/dry trickle, algae scrubbing and mud-based mediums.
Scavengers, which provide a biological benefit to the filtration system by consuming decomposing matter, are small bio-loads. Soft, small and large polyp corals are light bio-loads; they do not consume a large amount of material. Anemones however, are heavy bio-loads. Their feeding requirements equal that of fish.  The bio-filter breaks down the bio-load. 
References1. http://www.reefland.com/forum/saltwater-fish-only-aquariums/21161-what-your-system-bio-load.html2. ^ Hauter, Debbie; Stan Hauter. Nitrifying Bacteria Population VS Bio-Load Ratio Reactions (HTML). Saltwater Aquariums. About, Inc.. Retrieved on 2008-03-17.  External links
* http://saltaquarium.about.com/library/blank/blbac_bioloadchartlight.htm Bio-load ratio]
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