There are many questions about the various devices being recommended, especially when it comes to Reefs. My suspicion is that, aquarists, by and large, have not adopted that 'research first' mentality, so needed, for such a complex subject area as SW aquaria. In this area I am going to discuss the practical aspects and functions of equipment widely recommended, and many times inappropriately done so. Some individual brand names will be discussed, but my experiences are limited, and I, as others, do rely on experiences of others, in many cases, also thankfully, for additional recommendations.
The phenomenon of complete biological filtration, (denitrification) the reduction of toxic nitrogenous waste, ammonia, nitrite, nitrate, to harmless constituents and nitrogen gas, takes on a totally different path then conventional nitrification, the production of nitrate. Without getting into complex processes, simply the establishment of a deep sand bed, layered with differing grains of calcerous materials, where one layer is, "LiveSand" and where water flow, adequate to penetrate at least one-half of the sand bed, is sufficient to establish denitrification. Its as easy as that! You don't need to be a Rocket Scientist or Brain Surgeon! The principles are amazingly simple, and actually comes from what "Nature' is doing in the ocean.
Although recommendations for sand bed depths varys considerably, ideally a SandBed should be 6 to 8 inches deep, which is not always practical, feasible or even 'sightly' in most small tanks, so 4 to 6 inches should be sufficient. Deeper is still better.
Bottom layer: Consists of approx 2 inches in depth of Aragonite (any brand) of coarse size 2 to 3 mm grain size. Here's a simple calculator to determine the amount of sand for any tank. Take the length and the width of your tank's bottom. For each square foot of area, depending upon the grain size of your substrate material, you will get one inch of sand bed depth for every 8 to 10 lbs of material. For the larger grains, calculate 8 lbs per square foot per inch, and LiveSand and finer grained and oolitic sands, 10 lbs per inch per square foot. Your LiveSand layer should also be around 2 inches. The uppermost layer is composed of a combination of finer sand, called oolitic, and aragonite of .05 to 1 mm, mixing these two grain sizes.
The mixing of two sizes, one coarser then the other is important, because one needs a lot of water motion to insure proper oxygenation of the top layers of the sand bed, which, if only using very fine sand, would be blown around. As a simple calculator, a 100 gal tank has approx 8 sq. feet of bottom area. To construct your DSB, to the optimum depth of 6 inches would require approx. 128 lbs of coarse aragonite, followed by anywhere from 120 to 130 lbs. of LiveSand, and covered with a smaller grained sand combination of 65 lbs of oolitic and 65 lbs of .05 - 1 mm aragonite. There are no hard or fast rules about sand construction, as far as differentiation between grain sizes, and many aquarists, especially those who have access to Southdown� Tropical Playsand�, which is aragonite distributed by Home Depot� stores, available at a much lower price, then traditional aquarium stores, can use 2/3 of this amount (approx. 260 lbs, with 130 lbs of LiveSand sandwiched in-between. Some aquarists would opt for a shallower substrate of 4 inches in depth, which would calculate out at approx. 175 lbs of Playsand� and 85 lbs. of LiveSand, sandwiched between two equal layers. There has been some questions of the quality of LiveSand as its purchased from a LFS or Mail Order. For the most part LiveSand, although rich in bacterial colonies, has been found lacking in sand sifting animal life. Its recommended along with the purchase of LiveSand, one should also get an assortment of infauna animals known as detrivores, separately, to complete your LiveSand denitrifying substrate. That's it, a denitrifying sand bed, no mysteries!
Of course, to complete the picture, you want: LIVEROCK: And thats fairly easy too. Here's the how to: We have to back step to our sand bed construction. Many aquarists place their rocks on the bare bottom, which is fine, others place them on top of the first layer, and pour the rest around them. A third option is to just lay some rocks on top. In this case rocks are known to sink into the substrate, and when stacked to the top, as many aquarists do, might result in an avalanche of cascading rocks. Something you do not want to happen! Some aquarists also use BaseRock, basically any suitable SW aquarium rocks which form the foundation for LiveRock stacking and placement of corals heads, etc. I suggest the BaseRock being placed atop the coarse first layer, and then placing pieces of LiveRock on the BaseRock, start layering the additional parts of the substrate. Its important that this is all done with sufficient water in the tank to cover each layering being done, whether substrate or rockwork. Now back to LiveRock. For a really impressive Reef tank, which will be heavily loaded with all types of corals, and other invertebrates, its recommended to get 1� to 2 lbs of LiveRock for every gallon of tank capacity, so your 100 gal. tank should have approx 150 to 200 lbs of LiveRock. If your going to have some fish, and want some swimming space for them, caves, etc. then 1 to1� lbs per gallon is sufficient (thats 100 to 150 lbs).
The other things you need is a Protein Skimmer designed with your tank's gallonage in mind. In fact the PS's capacity should be about two or three times turnover of your aquarium's gallonage, or even more, and water circulation without ANY mechanical interference. The ideal method, that not only aerates the water, but provides for detritus entrapment, a place for a Protein Skimmer, and strong current flow, so vital in a Reef system, is the use of an overflow, in conjunction with an under-the-tank sump, and a powerful water pump, for water return. Additional water movement can also be accomplished by placing various water pumping devices inside the tank, to direct water in different directions. It is vital that water movement occurs not only at the surface (easily accomplished by the overflow), but water movement directed in the middle and the bottom of the tank. If internal power heads are used, care should be taken to enclosed the inlets, so unwary animals will not be sucked into the powerheads. The desired rate of water turnover should be (on paper) at least ten times the stated gallonage of your aquarium, I prefer twice (twenty times your tank's gallonage) that amount. There are no hard or fast rules, but care needs to be given as not to move the substrate material around the tank, or disturb sessile life forms, yet water sufficient movement to facilitate biological processes, and keep your animals 'happy'.
The use of rotational devices, to simulate the to and fro motion of water currents in reef zones is the ideal method, and is also highly recommended. Various device are available, including rotational power heads, electrically operated oscillating water outlets, and various devices that use water pressure, to generate motion. Some entrepenuring aquarists have used modified rotational water sprinklers to create motion in their tanks. Be aware that all metals have to be removed from them, and they do restrict water pressure in order to make them rotational. One such device is a ReefRotor� from Hunter Industries�, various power heads and a rotational device made by Rio�, plus an electrically driven unit known as a SeaSwirl�. More complex systems that employ containers that dump water in your tank at a regular rate, known as surge generators, are available, either as DIY projects or ready made, as the SilentSurge� device. Search engines are useful to find these DIY and informational web-sites, as www.infoseek.com or www.chubba.com
Sufficient lighting to accomplish photosynthesis for those animals that require it. Without going into the meaning of Kelvin temps, the way lamps are designated, its sufficient to say that Sunlight, strikng the ocean's surface has a Kelvin temp of 5800�K at high noon at the equator. As sunlight penetrates sea water most of the light rays corresponding to colors ranging from red, orange, and yellow, for the most part are filtered out. What's left is the greens blue, violet and ultra violet rays. As far as the aquarist is concerned, lamps with Kelvin designations between 5800�K and 12,000�K compromise 99% of the wave lengths used by photosynthetic animals. As far as wattages are concerned, approx 4 to 5 watts per gallon is required by so called 'low light' animals, 7 to 8 watts per gallon for medium light animals and 10 to 12 watts and more for high light animals. Research has shown that this 'rule of thumb' works for most cases, when balanced spectrums are also being considered. Now its true that animals will live under lower light conditions, but they will not thrive and multiply as readily, as when lighting is tailored to meet their natural demands.
There is no general agreement as to what wattages to use, especially when highly photosynthetic requiring animals are being kept or desired. I have read that wattages anywhere from 4 to 5 watts/gallon, up to my recommendations of 10 to 12 watts/gallon. You need to do further research into lighting in your choice of lamps. Even where Kelvin temps are discussed, where 6500�K to 10,000�K appears to be ideal, some authors recommend lghting temps between 12,000�K and 20,000�K. For the most part higher Kelvin lamps are more for the 'taste' of the aquarist, rather then of real benefit to photosynthetic animals. There is much experimentation and trial and error needed, for successful Reef keeping.
One other desireable requirement is the simulation of morning, noon, and sunset lighting periods corresponding to the natural cycle of the sun. This is not always easily accomplished. However, with independent wiring for each lamp, and timers, this can be done with a minimum of expense and effort. Some aquarists employ very low wattage 'red' or blackights, to simulate moonlight, so they can observe the myriad life forms that emerge in the dark. Now there's your Reef, no mystery, no ugf, no canister filters, carbon, resins, wet/dry with bio-balls. Just LiveSand, LiveRock, Skimming, Water movement and Lighting. Any Questions?