Just as live rock forms a very efficient natural biological filter, sandbeds can also contribute greatly to natural filtration in the saltwater aquarium. Aragonite sandbeds also help buffer pH, keeping it more stable.


Sandbeds Add A Natural Look To The Aquarium

In this page, we will discuss both shallow and deep sandbeds.

Shallow Sandbeds And Why You Need At Least 3 inches Of Depth

A sandbed of less than 3 inches would do little to act as a natural filter. Its function would be mostly aesthetic as it would be too shallow to harbour anaerobic zones — oxygen poor areas where nitrate reducing anaerobic bacteria can reside.

Some aquarists choose to go with a very shallow sandbed of less than one-inch of relatively coarse sand that will not get blown around by powerheads. Very shallow sandbeds are mostly for aesthetic purposes, serving no biofiltration function. This is also fine as live rock will serve as the main biofilter.

Shallow Sandbeds And Excess Nitrates?

It has been suggested that if the depth of a sandbed is somewhere between one-inch and two-inches, excessive nitrates will occur over time. This is because only aerobic bacteria live shallow sandbeds. And as we know, aerobic bacteria only break down nitrite to nitrate. Without the presence of oxygen-poor layers and anaerobic bacteria, the nitrate will not be converted to nitrogen gas, causing an accumulation of nitrate over time.

In my experience, shallow sandbeds may become a nitrate sink only if you don’t have enough live rock in your tank. Live rock is an excellent biofilter, harbouring both aerobic as well as anaerobic bacteria, and is usually enough to take care of any excess nitrate that a shallow sandbed might produce.

If you don’t want to take chances with your sandbed, I highly recommend a depth of 3-inches all around.

Deep Sandbeds

Any sandbed that is deeper than 4-inches would qualify as a deep sandbed.

A deep sandbed — one that is at least 4 to 6 inches in depth — provides an anaerobic zone for denitrifying bacteria which effectively convert nitrate to nitrogen gas.

There was a fad a few years ago when aquarists went for very deep 6-inch sandbeds. The understanding at the time was that the deeper the sandbed, the greater the anaerobic area for nitrate reduction.

Problems With Deep Sandbeds

The deep sandbed fad lasted until some aquarists began to report areas of blackened sand visible through the glass or under live rock when it was moved. These blackened, anoxic areas had a distinct odor of rotten eggs and were caused by a buildup of hydrogen sulfide.

Small patches of hydrogen sulfide do not pose a serious problem provided there is enough water volume to dilute the situation. But it was enough to alarm many deep sandbed enthusiasts so much that it made them siphon out all of their sand and go barebottom instead!

Not exactly the most natural look for the saltwater or reef aquarium.

Some aquarists running older tanks with deep sandbeds have also reported accumulated nitrate being released from the sandbed and back into the water. Most of these aquarists had deep sandbeds that had been running successfully for years with near zero to minimal nitrates, only to experience a high nitrate spike after the fourth or fifth year of the tank’s life.

As you can probably tell by now, I am not a fan of deep sandbeds..

Live Sandbeds

When you add live rock to your aquarium, tiny worms, brittle stars, copepods and other microfauna find their way into the sand, making it ‘live’.

The worms and brittle stars burrow into the sand, consuming detritus, while the copepods multiply and become a valuable food source for corals and fish.

When setting up a new tank, I always take a few cups of live sand from a mature aquarium and sprinkle it in the center and along the four corners of the tank. This helps the new sand become a live sandbed more quickly.

A Word About Packaged ‘Live Sand’

Commercially available ‘live sand’ is packaged sand that is bagged wet. Most come with the dangerous claim that no cycling of the tank is needed.

Such claims are not to be taken seriously and are part of the product’s marketing hype — there are no miracle, instant shortcuts to properly cycling a new aquarium.

I have used these live sand products before and found the sand to be of high quality, but that is the most I will say about it. I found that I was paying for the bagged water as much as I was paying for the sand.

Read More About:

Live Rock

pH And Alkalinity

Nitrate In The Aquarium

The Nitrogen Cycle



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