Sand Or Crushed Coral – Which Is Better For Your Aquarium?

Most of you coming from freshwater will have been used to gravel as the substrate in your aquarium, but now you are faced with a plethora of substrates! Which do you use? What grain size? Which material?

There is a great range of substrates to pick from and this article is here to help you decide which substrate will be best for your aquarium.

Crushed coral was a popular substrate choice for many aquarists but newer sand-based products help reduce trapped detritus, balance Ph better, and a wide selection of grain sizes to suit every aquarium have made sand become the preferred choice for saltwater aquariums.

What Is Crushed Coral?

Crushed coral mainly consists of a mix of limestone, coral skeleton pieces, and shells. It was a substrate that was very popular over ten years ago with saltwater aquarists.

It has large grain sizes which makes it good for tanks with very high flow. Smaller grain-sized substrates can be whipped up by a strong flow and create a sand storm in your aquarium. This was prevented by using the larger grains of crushed coral.

Because of the larger grain sizes of crushed coral, it does present a different problem! It is notorious for trapping uneaten food, excrement, and dirt; often referred to as ‘Detritus’.

Typical Crushed Coral

The detritus is able to settle into the gaps between the grains and if it is not removed by regular maintenance of the sand bed, it will begin to decay and break down. As the detritus breaks down it will release Ammonia, Nitrates, and Phosphates which will feed algae.

Many aquarists have reported tank-destroying algae outbreaks many years after their aquarium was first installed. After removing the detritus-laden substrate and replacing it with a sand-based substrate their algae bloom dissipated.

Another problem with crushed coral substrates is that you will not be able to purchase any sand-sifting animals as part of your Clean-Up-Crew.

Sand-Sifting Starfish, Goby’s & Nassuarius snails all like to bury themselves in the sand and sift it through their mouths to help remove the detritus. The grain sizes in this substrate are too large for these animals to work in your aquarium.

Crushed Coral is a dated substrate that is very rarely used today. There are much better alternatives that allow you to maintain a cleaner substrate to prevent the buildup of detritus.

What Is Dry Aquarium Sand?

Dry sand is just what it sounds. Sand that has been collected, dried, and then packaged. The majority of sands available for the saltwater aquarium are all aragonite-based (More on this at the end of the article) and CaribSea is the major producer that you will find in most saltwater aquariums in North America.

Caribsea sieves the sands into varying-sized grains to suit your particular requirements.
You can get sand in fine ‘sugar-sized’ grains which Caribsea recommends for Deep Sand Bed aquariums where Anaerobic zones are required for Nitrification.

They also create large grain sands for those SPS dominant tanks that required very strong, random water flow that could send the small-grained sand flying all over thank tank.

With varying grain sizes between their two extremes, you can find a sand to match your requirements.

Dry sand takes a little while longer to cycle because it has no beneficial bacteria within it, but for those of you who wish to begin with a completely sterile aquarium, dry sand with dry rock is the perfect way to go.

What Is Live Sand For An Aquarium?

Live sand is the same type of sand as dry sand except it comes packaged wet. Contained within this moisture are billions of broad-spectrum marine bacteria but also carefully selected strains of marine bacteria to help begin the formation of your aquarium’s biological filter.

Arag-Alive!™ is the benchmark product range from CaribSea that says exactly what it is. Aragonite sand that is alive with bacteria.

CaribSea Arag-Alive Fiji Pink Sand
Typical Live Sand

The two biggest benefits to using the Arag-Alive!™ range of sands is that the bacteria contained within it will allow a faster aquarium cycle due to the bacteria already being colonized and because it is Aragonite based it will keep the water’s Ph stable around 8.2 which is perfect for a reef tank.

The Caribsea Arag-Alive!™ range of sands is the brand I recommend, have in my own aquarium and have used in all the clients’ aquariums I have installed over the years.

You can view a nice selection of Live Sands HERE at

Can You Mix Live Sand With Crushed Coral?

But what if the aquarium you bought second-hand comes with a crushed coral substrate and the previous owner swears by it? Can you just clean the crushed coral and then add new sand to it to speed up the cycle? Well yes, you can but why would you? Saving money is usually the first answer I hear.

If you do add sand to a crushed coral substrate you will fill in all the gaps to prevent detritus from building up, but if you do not clean the crushed coral properly you have now just locked in that detritus which will decay and release its problem elements.

The other problem is your substrate will still be too coarse for any sand-sifting Clean-Up-Crew to help keep it clean.

The best practice is to dispose of the crushed coral and start with new sand, dry or alive. Just spend the little bit of cash now to install a new sandbed and save yourself potentially many nitrate and phosphate problems in the years to come.

It is far easier to remove the crushed coral now than to do it when the aquarium is full of life (and Algae!).

What Is The Best Substrate For A Reef Tank?

There are two main types of substrates available:

  • Aragonite from the Florida/Caribbean Areas
  • Calcite from the inland USA Areas


This is by far the most popular sand for saltwater aquariums because it is comprised of a type of Calcium Carbonate that will slowly dissolve in a solution of Ph 8.2.

This is important because most reef tanks like to sit at a Ph of around 8.0 – 8.2. As the Aragonite slowly dissolves, it releases Calcium Carbonate into the water which is then consumed by the invertebrates to build their shells and corals like LPS and SPS to build their skeletons.

Calcium Carbonate helps to maintain calcium levels as it dissolves.


This is also a calcium carbonate-based mineral except it dissolves at a much lower Ph of 7.5. With saltwater aquariums having a much higher Ph this type of substrate will never dissolve. Because it doesn’t dissolve in a saltwater solution of 8.0 you do not get the added benefit of the sand buffering and stabilizing the Ph.

Calcite is used more in freshwater aquariums were a lower Ph is aimed for.

Now you have the information to decide on what type of sand is going to be right for your aquarium the next thing you need to do is calculate how much sand you need to buy.

Click on the button below to go to Bulk Reef Supply’s sand bed calculator. It gives you some great information on the types of grain sizes and then calculates how much sand you need to purchase

↓ ↓ It Is A Super Useful Tool!!! ↓ ↓

Further Reading

To help your research you may find the following articles helpful:


Hi, I'm Richard and I have been an avid aquarist for over 30 years with a passion for Saltwater Aquariums. I love to pass on my knowledge to help others get the same amount a pleasure out of this hobby as I do. View my About Me page to find out more about me & my mixed reef aquarium.

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