DEEP SAND BEDS 101
By Oceandose.
 

This is a brief rundown of setting up a DSB, how they work and things to do to make sure you have a fully functioning sand bed, not just a bucket of sandaccumulating sulphides and detritus. With all the confusing and conflicting articles on the net, I’ve just listed the basics that have been proven to work, and supported by the leading people on marine ecosystems.

Why add a DSB to your current system? 
A well functioning deepsand bed will keep water paramaters in check and even reduce nitrate to undectable levels, you will achieve amazing bio-diversity with many new worms/pod and micofauna growth not seen without a DSB. 
To make it even better, the DSB will also release planktonic lavae into the water column which will provide a food source for many corals/fish and other inverts that haven’t been able to thrieve with generic available food sources.
A DSB is simply the greastest addition to any setup, easily setup, low maintenance, low cost, very very effective.

“A DSB will help create an environment that will almost force your corals and other decorative animals to thrive. With some 35 years of experience as a marine ecologist behind me, I can say that THE most important component of a coral reef aquarium is a deep sand bed” quote from Ronald L. Shimek, Ph. D,

How does a DSB Work?
A properly functioning DSB can have hundreds of different organisms living in them and can be broken down to three separate and essential functions/areas.
The first is the aerobic region of the sand bed, this occurs in the top 1-2 inches of the sand bed and houses two types of bacteria, the first will convert ammonia into nitrite and the second will convert nitrite into non-toxic nitrate. 
Secondly you have the anaerobic region which is void of oxygen and usually occurs below the top 3-4 inches of sand, the function of this area is to host de-nitrifying bacteria. These bacteria have the important job of recycling nitrates that build up into nitrogen gas, the gas will then rise with help of the third process though thesand bed to the surface leaving the aquarium. 
So now we have a complete bacteria nutrient recycling factory built into our aquarium, but it wont function properly without the last area, 
Bioturbation is third process and is basically inverts and microscopic life burrowing though and turning over the sand. This ensures that the aerobic areas of the DSB are turned over frequently supplying more oxygenated water and nutrients to feed the bacteria in the zone. The same process also turns over the sand in the anaerobic areas, which frees the nitrogen gas trapped and allows more nitrate rich/oxygen deprived water to enter the zone for bacteria to feed on.
This is a truly fantastic natural filter, the small microscopic microbes; copepods, amphipods, bristle worms and the likes are all eating the excess food that lands on the DSB as well as turning over the sand to allow a continuous supply of fresh nutrients to the specific bacteria.
Once you have achieved these 3 areas of a DSB, you will have the most effective and complete style of filtration available, not to mention with ZERO running costs.

How to setup a DSB
We can setup a deep sand bed in many different ways, the best would be another tank plumbed to your current setup. It is also possible to setup DSB’s in buckets, but the surface area available to you will restrict the amount of Bioturbation and micofauna growth. The larger the surface area the more effective the sand bed will be, keeping in mind that we need to also achieve an anaerobic zone. To do this we will need to have our sand bed at least 4 inches deep, this is a bare minimum and recommend going for at least 6 for effective nitrate removal. There are a couple of university studies around that find no extra benefit going deeper than 8 inches, as bioturbation doesn’t occur.
The next part to consider is the sand grain size, basically put the finer the better. If you use coarse sand, you are actually creating a nutrient trap and will foul your water. The best grain size is 0.1-0.5mm, this suits the majority of fauna we host, if you had the option of setting up multiple sand beds, I would use a variety of particle sizes, as certain species wont just make do with the in-correct sediment size, they will just fail to establish themselves. You can increase your diversity further by having an environment that is suitable, i.e. different grains in different beds.
When we plumb the DSB to the tank, you want to have a good water flow going over the sand bed, but essential that the flow isn’t too strong to upset the surface of set the sand. The only movement in the sand must come from the fauna living and growing inside of it. Any sand can be used to build a bed calcium or silica, but particle size is what will make or break the deal, another part of the bed is the actual shape of the sand, you want sand that has been created naturally so that its smooth, crushed sand has sharp edges and is very abrasive on the fauna crawling though it, which in turn limits the amount of bioturbation again.

There is a big misconception regarding hydrogen sulphide, yes it is produced in the lower levels of the DSB by the de-nitrifying bacteria, but it WILL NOT migrate up to the top layers and enter the aquarium water, once again bioturbation will release any trapped nitrogen naturally, There is also NO evidence that hydrogen sulphide can reach fatal levels in a DSB. You will eventually get black stained sand in your sand bed; this is a combination of sulphide build-up (which de-nitrifying bacteria eat) and many other metals such as manganese (black), iron (red/brown), etc. into harmless manganese oxide, iron oxide, etc.

A major part of a successful DSB is the inverts/micofauna and pods, which include
many types of flatworms, round worms, dozens of species of bristle worms, small snails, brittle stars, small sea cucumbers, protozoans, and many types of small crustaceans. A great idea is to seed your sand with a bit of a friends, and likewise swapping sand with friends occasionally to keep a good variety of life in your bed.

Under no circumstance should you stir/turn the sand manually or add sand sifting fish to turn over the bed, they will eat all fauna and kill the sand bed, these fish are specifically for the display. The DSB should be closed to all predatation from fish, think of it as a refugium with a pile of sand at the bottom.

Happy deep sand bedding, it’s the greatest addition to your tank and just as impressive to watch.