DSB - Deep Sand Bed Potential Anthony Calfo For many years, we have seen the use of substrates in marine aquaria wax and wane in popularity. The issue has run the gamut from bare bottom through shallow bed to deep sand, and then back to bare bottom again. But even with the acceptance of truly deep sand beds in America by the mid 1990’s, DSBs did not see regular use until refugia were established some years later. The reasons are obvious, perhaps: refugia are smaller, more affordable and less risky “models” of deep substrates, which the average hobbyist can attempt with greater confidence. But even with fears aside, the addition of a deep sand bed to a full display (versus a small refugium) is an investment in labor and money. It is no wonder that the large-scale DSBs took some time to be accepted. As the popularity of DSBs grew, the number of critics did too. Sadly, many of the most outspoken detractors argued in theory without even trying a DSB! And the majority of the rest of the critics seemed to unfairly blame their aquarium failures on their very limited DSB experiences. The more likely cause of their failures was from typical bio-overloads, poor water flow, and neglect of water quality. The reality of successful DSP applications, however, is amazingly simple, albeit strict. For perspective, I can tell you that my experience with living substrates is not insignificant. I utilized 48,000 lbs (over 20,000 kg!) of fine sand for my coral farming greenhouse operation and have installed similar deep sand beds in over one hundred private aquariums for over ten years. In this article, I will share with you a very practical survey of the potential - and the limitations - of a deep sand bed application. If I had to reduce the summary of challenges of deep sand bed applications to a single statement, I would have to say that new hobbyists have unrealistic expectations for what a deep sand bed can do. That is not to say that a deep sand bed does not have great potential! They truly do. But many people seem to have extremely high expectations for new sand to become teeming with life almost overnight in aquaria. Such a thing is difficult and requires careful orchestration, time and patience to happen. But more often, it fails because of impatience; aquarists stock DSB aquariums too quickly with predatory fishes that consume the foundling populations of desirable worms, microcrustaceans and other sand fauna, before the sand life can adequately populate to sustain predation. That is an enormous mistake. The inferior biotic faculties struggle to process the all-too-common overload of fishes, food and waste in aquaria, and the DSB fails in such circumstances. A similar problem occurs in DSB systems with inadequate water movement that allows too much particulate waste to sink and accumulate excessively in the DSB over time, causing the aquarium to “crash.” Instead, we should aspire (in bare bottom and DSB aquaria alike!) to always keep reef-like water movement with strong flow that keeps solid matter in suspension longer for greater feeding opportunities by the filter feeders and better processing by skimmers and other filters. Strong water movement in the aquarium is the number one key to success with long-term healthy DSBs. I recommend “sps-style” water flow of near 40-60 X turnover of the tank display for best results. I can remember in the early days of reef-keeping in America, we would hear stories of great German aquarists that would keep their new live rock (for “Berlin” style systems) in the dark for six months or more with good water flow and supplementation (organic and inorganic). The purpose was to dramatically improve the quality of “cured” live rock with greater coralline algae and more life forms before lights and fishes were applied. Few American aquarists had the patience to do this at the time, but I think we must have admired the German stony coral displays so much and remembered the lesson that we apply it now to our refugia and DSBs. Now, with thanks and respect, we remind our European friends of this same patient advice: avoid adding predatory fishes or corals to DSB systems for many months to allow adequate populations of infauna to develop. You will notice that these two fundamental pieces of advice are different from what most retailers and so-called experts will recommend. Both mistakenly tell you to add “clean up” organisms from the very beginning (note: at least one of those two people profit from this bad advice  ). But the addition of predatory snails such as Whelk (Buccinid), Murex (Muricid), Mud (Nassarid) and Tulip (Fasciolariid) can be devastating to the desirable life forms in the sand of an aquarium. The popular Conch species (Strombids) are even worse as most will starve to death not long after they have decimated the infauna of a DSB. Of similar concern is the use of Holothurid “Sea cucumbers” (and Sand-dollars) and all of the sand-sifting gobies. These vigorous sifters destroy a lot of biomass in the substrate. Worst of all perhaps are the alleged “reef-safe” hermit crabs; these crabs are brutally indiscriminate predators on desirable sand bed life forms. The only thing that any of these aforementioned “bad” DSB organisms are actually good for is tilling the sand surface to prevent the buildup of brown diatom algae. But you can use a number of safer organisms to accomplish algae control without destroying DSB biodiversity! Best bets for DSBs include: Stomatella-type “paper shell” snails, Ceriths (Cerithium and close kin) and most all errantiate polychate worms. Yes… “bristleworms” are very good. They are rate-limited in population by available food, which in turn is rate-limited by good water flow that prevents excessive solid matter from settling and accumulating over time (back to rule #1 above regarding adequate water flow). In time, you may even allow small Asterina-type sea stars to flourish (this is somewhat controversial, but they are generally harmless, if not helpful). For starfish, Ophiuroid species (Brittle or Serpent starfish) are perhaps best of all for being low burden, low maintenance and high utility as scavengers. After a year of establishment, various ornamental shrimps, such as Lysmata, may also be added; their benefit (producing larvae as food for corals) may balance with their burden (preying on DSB fauna). And for fishes, perhaps the best “clean up” group is the bristle-tooth tangs of the genus Ctenochaetus with their specialized mouthparts that comb diatom algae from the soft sand with little burden otherwise on desirable sand fauna. Manual sand stirring by the aquarist, though, is not needed when adequate water flow and livestock are in place. That said, manual stirring can be helpful for feeding some specialized filter feeders or extending the life of the sand bed when water flow is not ideal in support. In time, you will see various colored algae appear to grow substratum, but they are only existing in tiny films between the aquarium glass and the sand face; they are not growing throughout the sand bed. Such algae are often stimulated to grow in front because of the indirect room light and the aquarium lights reflected down through the vertical panes of the aquarium. Many aquarists with adequate water flow and good DSB maintenance have also noticed that while moving an established sand bed, the overall substrate is remarkably clean and odor free like the first day it was placed into the aquarium! This is exactly how a healthy DSB should be after many years. I personally moved a nine-year old sand bed (15 cm deep in a 1000 liter aquarium that held two small reef sharks) that made this very same impression on me: clean, odorless, healthy living sand. Perhaps the most underrated but also the most reliable and significant benefit to a DSB is the ability to reduce nitrates naturally and quickly. Over ten years ago I wrote about hobbyists using a remote DSB (AKA – “RDSB”) as a means of addressing the fears that many folks had at the time (and some still do) about “what if” a display DSB gets polluted or goes bad. It is true too; illuminated DSBs are more of a challenge to keep healthy because of the site competition (sand surface) between desirable and undesirable life forms with the increased availability of energy sources (food, waste, light). Yet, most all of the benefits of a DSB can be had with an unlit DSB reservoir that is plumbed inline to the main system. The typical RDSB application for home-sized aquariums (under 800 liters) is a large bucket full of sand (maybe 25 kg of fine sand in a 20 liter bucket) that has a supply of filtered water on a continuing path in the aquarium system. Some folks simplify it even further by sitting their RDSB bucket in an unlit sump and gravity feed water from a display or refugium above… or even a tee off of the sump pump manifold. The sump RDSB can then gently spill over the sides of the bucket into the open reservoir. It is quite simple and effective for mainataining nitrates below 10 ppm. However you choose to install an inline (R)DSB, you can estimate that approximately 25 kg of fine sand (< 2mm grain size) per 400 liters of aquarium water will fully, or nearly so, reduce nitrates in a typical bioload. For over a decade, aquarists at large have reported struggles to keep nitrate levels under 40ppm with large and frequent water changes and other drastic measures to no avail. But, after the installation of an RDSB, nitrates were reduced in less than 4 months with many showing significant progress in 8 weeks or less. I have even observed several retail stores with heavy bioloads in central filtration systems see their nitrates reduced to near zero with the installation of a sand-filled 200 liter RDSB aquarium (1mm sand grain size… full nearly to the top with only 10 cm of water flowing across the sand surface). This is effective on 4000 liter fish holding systems! The single greatest benefit of a DSB is nitrate control. While many aquarists like to claim through the years that higher nitrates are tolerated by many fishes, the reality is that many other fishes do not tolerate it well. Reports about Pterois, Sharks and other predators, for example, implicate high nitrate levels as inhibitory to iodine uptake, which can lead then to thyroid hyperplasia (“goiter” in the throat). The condition worsens in time to the point where the animal is unable to feed. Using the bucket RDSB as an example (versus refugium substrates or display DSBs), this is perhaps an illustration of all of the best and worst of a DSB application: - There is little risk and little gain (aside from great nitrate control) to healthy DSBs
- Strong water flow above a DSB will easily keep it healthy, poor water flow will quickly destroy it
- Anywhere you choose to install a DSB is simple and inexpensive, but laborious and cumbersome (space-consuming)
- Living sand is like living rock: great patience produces superb quality living substrates, but impatience (stocking with fishes/corals too soon) produces worthless living substrates
One of the great advantages to having your DSB remote in refugia or a bucket is that it can be turned offline or bypassed rather easily if special needs call for it. Medicating the main display can be difficult or practically impossible with an in-tank deep substrate that absorbs medication and kills off a massive amount of infauana. But a remote DSB can run fallow on a small loop of recirculating water while the needs of the display are addressed in cases of emergency. If the RDSB fails for any reason likewise, its removal from the system can be a simple valve turn away versus an enormous project of draining a tank for display DSBs. My recommendation is most always to keep your DSB remotely for these reasons and more. We must also consider the composition of sand used for DSB to support desirable life forms in and above the substrate as well as be supported by applied water flow. The “rules” for DSB sand are not very strict, but they are rather practical. When our stated goals are culturing low-oxygen faculties for nitrate reduction plus the minimal penetration of and accumulation of solids in the substrate over time, smaller sand grains are better suited for the purpose. I recommend sand grains under 2 mm in size for DSBs. Media that is larger than 2 mm can be used, but deeper beds and stronger water flow will be required to make it work successfully. Large sand grains allow excessive solid matter to penetrate deeper and faster and can lead to the problem that critics cite with DSBs becoming “nutrient sinks.” That said, a mix of large and fine grain sizes together can work if there is enough fine sand (< 2 mm) to fill the interstices. It is arguably better to mix DSB sands for greater biodiversity of infauna whereas a uniform grain size favors the dominant growth of certain organisms over others. Lastly, there has been a bit too much debate, in my opinion, over the intrinsic composition of DSB sands. The three principal choices are calcite, silica or aragonite. Each media type has its fans and critics alike. All, I assure you, can be quite similarly useful without nearly the difference in performance that the critics would lead you to believe. The fundamental thing to search for with any of them is grain size as per above, without much concern for chemical makeup. The advantages and disadvantages of each class of sand are as follows: Calcite DSB advantages: commonly available, moderately priced, wide range of grain sizes disadvantages: very little buffering ability over 7.6 pH Silica DSB advantages: very inexpensive from industrial sources disadvantages: no buffering, limited sizes (<1 mm), poor shapes (sharp and lacking fluidity) Aragonite DSB advantage: optimal shapes (oolitic and very fluid), excellent buffering pH, and mineral supplying disadvantage: generally more expensive and less available than silica or calcite Depending on aquarists’ budgets and access to choices among sand substrates, each composition listed above can be used and finessed appropriately. The oolitic (round/spheres) shape of aragonite affords the most fluid DSB that naturally churns and feeds lower zones while reducing diatom growth at the surface. Silica sand, on the contrary, locks its sharp grains and packs with very little movement. As such, solid waste is less likely to penetrate, for better and for worse (less food for biotic faculties), while diatoms can grow more easily at the surface. A silica DSB will be less expensive to install but more expensive (labor) to maintain… perhaps requiring manual sand stirring and greater water flow. Aquarium hobbyists usually find calcite sand beds to be the best choice for aesthetics, price, availability and required husbandry; all are moderate. With this primer, I hope to have provided you with a “noiseless” summary of the legitimate and practical expectations for what a DSB can – and cannot – do. If you can resist the extreme ends of the argument, I think you will find that this is a viable and reliable methodology for marine aquariums. With kind regards, Anthony Calfo
. Anthony Calfo
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