aquarium sand how to pick the right substrate for your saltwater aquarium

Aquarium sand: How to pick the right aquarium substrate for your reef tank

This article provides an overview of how to pick the best saltwater aquarium sand.

When I first started in the aquarium hobby a thousand years ago, the decision about what aquarium substrate to use was pretty simple. There were two options: fine sand or coarse sand (crushed coral) and two ways you could choose to place it in your tank.

You could either have a deep sand bed, shallow sand bed/bare bottom.

Those are still two of the more important parameters to consider, but the increased popularity of the hobby has created an opportunity for more options for us consumers. I think most people would agree that it is generally better to have more options than less, but having too many options can sometimes create a separate problem: how to pick the right substrate for your saltwater aquarium?

In order to answer (or at least inform) that decision, let’s take a look at what options you have available.

A few quick notes:

For the purposes of simplicity, and to avoid repetition, I’m going to consider the words sand and substrate to be relatively interchangeable, in this article.

The substrate is arguably any structural object in the tank (including the live rock), but in this case, since this post is about aquarium sand, please just assume that the substrate I’m referring to is sand, unless otherwise noted.

Here is what I will cover in this article about aquarium sand:

  • Types of aquarium sand
    • Aragonite
    • Crushed coral
    • Oolite
  • Aquarium substrate colors
    • Traditional
    • White
    • Black sand (Tahitian moon sand)
    • Pink sand
  • The function of aquarium sand
    • Aesthetics
    • Surface area (for biological filtration)
    • DSB (denitrification)
  • What is the difference between dry sand and live sand?
  • How much sand do you need?
  • How to add sand to your aquarium
  • What is the best sand for a reef tank?
  • Where to go for more information

Sand from Gobi Desert.jpg
Sand from Gobi Desert” by Siim SeppOwn work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

Types of aquarium sand and how to pick the best marine aquarium substrate

Aragonite -the most popular of the aquarium sand types

What is aragonite sand?

Aragonite sand is perhaps the most commonly recommended sand in the saltwater aquarium hobby. It is generally available as a fine grain product that “looks” like the prototypical sand. What makes aragonite sand so commonly used in the aquarium hobby is that it is made from the same stuff that coral skeletons are made of…calcium carbonate. In fact, the term aragonite sand is really just a fancy way to state…sand composed of calcium carbonate.

Crushed coral

Crushed coral aquarium sand, by comparison, is a substrate with much larger particles…instead of fine grains of sand, a crushed coral substrate looks like tiny white stones (that are actually pieces of crushed up coral skeletons…which is where it gets its name.


JoultersCayOoids” by Wilson44691Own work. Licensed under Public domain via Wikimedia Commons.

Oolite (also sometimes called oolitic aquarium sand), is usually just a ‘fancy’ type of fine, spherical aragonite aquarium sand. The term oolite refers to the way the sand was formed. Oolite sand is formed by ooids (shown in the picture above, which are spherical grains formed in concentric layers.

By definition, oolites have to be less than 2mm in diameter–which means that oolitic aquarium sand is composed of tiny egg-shaped to spherical grains of sand.

Because the term oolite technically refers to the size and shape, it can’t hurt to check the label of the sand substrate you’re thinking about buying (especially if you’re buying from a non-aquarium hobby source) to confirm the chemical composition, because it is possible to have oolite made from phosphate, hematite or dolomite.

Aquarium sand colors


aquarium sand

Can you spot the cuttlefish? Image by Raul654

You pretty much can’t go wrong with picking a traditional sandy color sand. I don’t have that much to say about this (and you can tell that what I have chosen to say, so far, isn’t all that articulate) but I didn’t want to overlook the most obvious choice. You could go with sand that looks like…well…sand. For a natural, functional and effective substrate, this is the straightforward choice.


If you are looking for a brighter look that can be achieved with the traditional sandy colored aquarium sand, you could potentially achieve a brighter, whiter color with a crushed coral aquarium sand substrate. As mentioned in the section above, this sand substrate is made from the (bleached) crushed skeletons of dead corals (that sounds bleak, doesn’t it), but out of the bag, it has an appealing white coloration. Be warned, however, the white color is most prominent on the dry substrate.

After some time, the white aquarium sand substrate will become covered in a biological film (ie. bacteria) and will also get clogged with dirt and detritus–so once your aquarium is up-and-running, your gravel won’t be such a pure white–but don’t worry, all that extra color (even though the color is mostly brown…) is actually doing good things for the health of your tank.

Black sand (Tahitian moon sand)

Black sand, sometimes marketed under the name Tahitian moon sand, because Tahiti is known for its black sand beaches, which were formed as a result of volcanic activity. Black sand is thought to form when hot lava comes in contact with the cold ocean water and breaks apart.

Pink Sand

The pink hue in pink sand is actually a combination of white and red. The white comes from traditional calcium carbonate (aragonite) sand and the red comes from the shells of a creature called forams–a tiny, single-celled creature that creates a hard, red skeleton/shell. When those creatures die, they leave their skeleton behind and give the sand a pinkish hue.

From a travel and vacation perspective, I think of Bermuda as being the most famous place to find pink sand beaches, but some of the commercially available pink sand products are said to come from Fiji.

The function of sand in an aquarium

Sand, in a saltwater aquarium, can provide one or more of the following functions:

  • Aesthetic appeal
  • Surface area for biological filtration
  • Substrate for burrowing or sand-sifting creatures
  • An area (potentially) for denitrification

Aesthetic appeal

I’m not sure if you’re the same way I am, but I create this pressure to know what all the stuff in my aquarium does…or is doing. I thought about starting off this section of the blog post with one of the more utilitarian functions that sand provides…but I realized that would do a disservice to what is probably the most important aspect of sand.

Sand, or another aquarium substrate in a reef tank, provides an aesthetic look and feel to a saltwater aquarium. It is the perfect complement to reef tank aquascaping and can help you achieve exactly the look you are going for–and after all, creating a beautiful reef tank is really what the hobby is all about.

So I encourage you to consider this aspect of aquarium sand as equal or more important than all of the other aspects…you might read the section on denitrification and think…wow…what a great benefit of keeping a deep sand bed…but if you’re not crazy about the big, nasty-looking sand bed…then don’t do it.

Use the sand to create the look you want. That is the first and foremost function. Treat any other benefit you get as icing on the cake.

Surface area (for biological filtration)

Biological filtration, in a saltwater aquarium, is performed by bacteria that grow on the live rock and on the live sand in your aquarium. Aquarium sand is a substrate with a lot of surface area and creates a perfect home for those biologically beneficial bacteria to grow on. But that doesn’t mean that you have to have a sand bed to have a good biological filter.

Plenty of aquarists are successful keeping reef tanks with absolutely no sand bed at all. These tanks are often referred to as bare bottom tanks. But plenty of life will inhabit your sand bed if given the chance.

Substrate for burrowing or sand-sifting creatures

Sand is also the home to a number of ocean creatures: engineer gobies and jawfish, shrimp, snails, crabs, and worms to name a few. There are also creatures that sift through the sand looking for a quick snack or a full meal. Suffice it to say…having the proper sand bed is critically important to keep these creatures. Plus, if you’re lucky, you’ll have a few unexpected and interesting guests take up residence in your sandbed.

Check things out with a red light at night.

DSB (denitrification)

If you have a sand bed that is at least 6 inches deep, you have what is called a deep sand bed. The advantage of having a sand bed greater than 6 inches in depth is that it is so deep that oxygen can’t get to the bottom layer of sand. There are bacteria that actually remove nitrates from the water that live in those anoxic (oxygen-free) depths in the sand.

So, an aquarium with a deep sand bed (either in the display or in a refugium) can not only turn ammonia into nitrites and nitrites (in accordance with the nitrogen cycle), but it can also remove that nitrate from the water column altogether (denitrification).

aquarium sand how to pick the right substrate for your saltwater aquarium

pH buffering capability? Not quite

One of the reasons often touted for picking aragonite sand is because the aragonite will dissolve and provide some additional buffering capacity to the aquarium. This is not true. Check out my article on the truth about marine aquarium sand.

What is the difference between dry sand and live sand?

Dry sand vs. live sand

One aspect of purchasing aquarium sand that can trip some people up is the decision about whether to buy dry sand or live sand.

As mentioned in the previous section, one important function of aquarium sand is to provide a surface for the bacteria that perform biological filtration in the tank to grow on. Those bacteria start to grow on your sand very soon after you set up your aquarium. Once your tank has completed cycling, there is probably a fairly robust population of bacteria growing on all the surfaces under the water. But cycling takes.

One way to shortcut the time it takes to cycle your tank and grow your own bacteria naturally is to purchase live sand, instead of dry sand.

Live sand is sand that has already been colonized by helpful bacteria. The sand is packaged and shipped ‘wet’ and with biologically active bacteria.

Compared with dry sand, live sand can be expensive…but if you must get your aquarium up, running and filled with livestock immediately, it can be a time-saving product.

How much sand do you need for a reef tank?

Another popular question is how much aquarium sand do you need for a reef tank? And the age-old answer to that question is…it depends. It depends on what you’re trying to achieve.

  • If your goal is to follow the aesthetics, then truly follow your intuition and go for the depth of sand that looks right to you.
  • If you are absolutely a rule follower and want me to give you a rule-of-thumb, you can start by aiming for ‘about an inch’, or 1-2 inches in depth. That seems to be a popular and aesthetically pleasing depth of sand to a lot of people.
  • If you want to have a deep sand bed (DSB), the rule-of-thumb that I learned, is to have a sand bed that is at least 6 inches deep. If your tank is only 18 inches tall…that’s a lot of sand…you may want to reconsider that. If you are going for a deep sand bed, you also want to be careful to avoid the no-mans-land between 2 and 6 inches. The chemistry that goes on during the denitrification process can be pretty nasty–and you don’t want that stuff stirred up into your tank accidentally. Having at least 6 inches or less than 2 inches of sand helps you avoid that problem altogether. If you want to learn about what goes on in the anaerobic environment, you can find that here

How much sand per gallon?

Now that you have a general idea of how deep of a sand bed you are aiming for, how do you know how much aquarium sand to buy? To figure it out exactly, you need to calculate the volume of that part of your aquarium (1-2 inches across the bottom) and do a conversion to figure out what weight of sand you need to fill that volume.

It’s not difficult math…but it’s a little involved. But why do the math, when you can use a ‘close-enough’ rule-of-thumb?

To get approximately a 1-inch layer of sand in your tank, you probably need about 1 pound of sand per gallon. So if you have a 10-gallon tank, shoot for about 10 pounds of (dry) sand. If you have a 55-gallon tank, aim for about 55 pounds of sand.

Now, actual results will vary, based on the shape of your aquarium and the size and shape of the grains of sand (coarse sand will take up more room for a given weight and fine sand will take up less room for a given weight), but if you start with that rule-of-thumb in mind, you can get close to your desired depth and then tweak it higher or lower based on how it looks in your tank.

Consider 1 inch per gallon or more than 6 inches per gallon and a rough, rough, rough approximation of a pound per gallon (to get 1 inch).

I’m the type of person where close enough is good enough, but if you’re the type that needs an exact answer–I encourage you to check out this online calculator. It looks intimidating, but it is fairly easy to use, and this will tell you exactly what you need.

How to add sand to your aquarium

The first step is to clean the aquarium sand. Believe it or not, the sand you buy (if dry sand) tends to be full of dust. The dust, if you put it in your tank, would make your tank horribly cloudy and ugly. To clean the sand, simply pour some into a bucket, fill the bucket part of the way with water, reach in and stir the sand with your hand. The water in the bucket will look cloudy and gross. I just keep rinsing and stirring until the water is clean.

If you are just setting up your aquarium for the first time, just gently scoop the sand with a plastic cup or a sturdy (non-breakable bowl) and add the sand to the bottom of the tank. You want to be careful not to ‘dump’ large quantities in a single area so you don’t stress and break the glass.

If your tank is already set-up and you want to add sand to an established aquarium, the technique is a little different and is illustrated in the video below. You essentially scoop it into a cup or bowl, lower the bowl all the way to the bottom and then gently turn it over as close to the bottom as you can. If you ‘dump’ the sand in from the top of the tank (and don’t do what I just described) your water will be a lot cloudier.

Check out the video below for a visual of how to clean and add sand to your aquarium. Please note, the tank shown appears to be freshwater, but I wouldn’t do anything differently than shown.

What is the best sand for a saltwater aquarium or reef tank?

The answer is…that depends.

Don’t let all the options and the commonly traded information cloud your decision.

Picking the best sand for a reef tank is as simple as figuring out what you want…and then doing it. Figure out what kind of look you want, and purchase a type of aquarium sand that gives you that look. Figure out what depth you want, follow the pound-per-gallon estimate, and add that much sand.

You want to try and avoid the no-mans-land zone between 2 and 6 inches (either be less than 2 or more than 6). You also want to pick an inert sand (aragonite or silicate). If you have more money than time, buy live sand instead of dry sand. It’s hard to go wrong when picking aquarium sand.



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