What is Kent Marine Biosediment?

by CR Brightwell, Marine Scientist

What is Marine Biosediment?
Kent Marine Biosediment is a blend of aragonite, calcite, and other minerals; it is not any mere aragonite substrate.  Marine Biosediment has been formulated in ratios that not only provide a much more natural substrate composition and density than using plain aragonite alone, but also to slowly dissolve as a result of natural solubility and close-proximity bacterial respiration, simulating the processes at work in sediment found on reefs, in lagoons and sea grass beds, and around mangroves.  Rather than being a blend of terrigenous (terrestrial in initial origin, i.e. silica sand, humus, etc.) particles, Marine Biosediment is composed of minerals naturally occurring in the afore-mentioned marine habitats, and therefore brings the aspiring hobbyist one step closer to providing his/her aquarium inhabitants a truly representative piece of the ocean. Over time, Marine Biosediment slowly releases trace amounts of calcium and other elements due to microbial processes taking place below the surface of the substrate; again, this simulates natural cycles taking place in benthic marine ecosystems. To calculate the number of pounds of Marine Biosediment needed to obtain a particular sediment depth in a refugium, follow this formula:

(Refugium L (in.) x Refugium W (in.) x Desired Depth of Marine Biosediment (in.)) x 0.05 = # lbs. Biosediment needed

Use of Marine Biosediment in Refugiums
Refugiums are becoming more and more popular in the marine aquarium hobby these days, as aspiring hobbyists attempt to maintain their closed systems with “natural filtration”.  A refugium is in essence a microcosm in which nitrogenous and organic waste is remineralized by algae, bacteria, microbes, and epibenthic invertebrates in the same manner as that found in the ocean.  Additionally, a refugium provides small and larval invertebrates sanctuary from predators, such as fish, that inhabit the system by physically separating them with an impassable barrier.

Constructing a refugium is a relatively simple undertaking; all that is really needed is a spare aquarium or sump (referred to as the refugium from herein) and an appropriate light source.  In this refugium, 2-3” of Marine Biosediment (discussed in detail below) are placed, which may or may not be “seeded” with bacteria and invertebrates by adding a few pounds of fresh “live sand”.  The decision to add live sand is up to the hobbyist, however, doing so will speed up the rate at which the Marine Biosediment becomes inoculated with beneficial microbes.  To this “sand bed” the hobbyist is advised to add a small culture of fast-growing macroalgae, such as that of the genus Caulerpa (check to be sure that Caulerpa is legal in your area before purchasing it for use at home; in the event that Caulerpa is illegal, you might substitute Penecillus or some other type of macroalgae).  Anchor the macroalgae firmly in place (in the center of the refugium, where it’s less likely to get covered in silt or blown around in the current), and allow water from the main system to flow through the refugium.  The goal is to create a steady, slow flow of water from one side to the other (i.e. water enters one side of the refugium and exits on the opposite side).  The flow rate should be slow enough to keep sediment from blowing up into suspension; this rate depends on water input tube placement, distance from the pump or source of water, etc.  Colonial polyped-invertebrates, such as octocorals, zooanthids, xeniids, and gorgonians, as well as some soft corals and scallops can also be housed in the refugium, as long as the lighting is appropriate, which brings us to lighting…

The refugium has photosynthetic life forms in it, requiring some form of light.  It is recommended that power compact fluorescent lights be used, as they take up little space, don’t draw much power, and remain cooler than VHO and metal halide lamps.  One thing to remember is to never, never, never run the lamps 24 hours a day… NEVER!  Just like plants, algae need a break from photosynthesis, and keeping the lights on all day and all night will cause the algae to enter a reproductive phase (i.e. they turn milky-white and disintegrate, releasing nutrients back into the system and lowering water quality).  The best idea is to have the refugium lights (a pair of 6,500K tubes is usually ample) on 8-10 hours a day, or rather night (when the lights in the main aquarium are off).  In a cycled system the hobbyist will notice rapid growth of the algae, indicating that they’re doing their job efficiently.  Every couple of weeks, remove a small portion of the algae, and either throw it away or sell it to someone starting a refugium; do not, under any circumstance, feed the algae back to the fish in the main system, as this merely redistributes much of the nutrients and waste that the algae have cleaned from the system!  Removing algae simulates grazing, and helps export nutrients directly from the system, making it a much cleaner, healthier place for the inhabitants.