Best Substrate For Saltwater Tanks

The use of substrate in saltwater tanks is somewhat of a hot topic and is often talked about and disputed among hobbyists. The reason being that there are so many different opinions on what looks the best, what works the best, do you need to use substrate, and so on.

There are many different options available when it comes to choosing a substrate for your saltwater tank. There are also many questions that are important to answer before you decide on purchasing a substrate.

In this article, I will answer some of the most important questions and explain what you need to know about the best substrates for saltwater tanks on the market today.


Do you need a substrate in a saltwater tank? What is it’s purpose?


The answer is no. You don’t need a substrate in your tank. In fact, many people prefer not to have it. I have had many bare bottom tanks, and they do have their advantages. One is the fact that it is easier to remove detritus and some people like the clean look. Also if you have a tank that requires high water flow, for example keeping SPS corals, you may not want a substrate that will blow around the tank.

There are a few reasons why you may want to use a substrate in your tank. One is that it can be very visually appealing. It looks more natural than a bare bottom tank. Reef substrates are available in different colors, types.

Substrates are used for biological filtration. Sand provides the surface area for bacteria to colonize. Some people will even incorporate a sand filter on their tank as they are very effective.

Sand is also very important for certain livestock. Sand sifting creatures or fish that like to burrow need sand in the tank in order to sift or burrow. The sand sifting Goby is a good example.

Sand is also used for deep sand beds (DSB). Deep sand beds are 6″ deep or more, and are used for denitrification. According to Marine Depot, “Using a deep sand bed with fine grain sand is great because of the increased biological filtration. It will promote both aerobic and anaerobic bacteria helping to break down waste and remove nitrates. A deep sand bed is typically 6″ to 8″ deep. Within the first 2″ to 3″, aerobic bacteria will thrive and help breakdown waste and produce nitrates. As you go deeper into the sand bad, the water will be less oxygenated and therefore anaerobic bacteria will thrive. This type of bacteria is very efficient at denitrification which will turn nitrate into nitrogen gas.”

I will explain the pros and cons of each below.

What kind of sand should you use in a saltwater tank?


If you decide to use sand as a substrate in your tank, you have a few choices and there are pros and cons of each. The most commonly used sand in a saltwater tank is Aragonite sand. It is fine sand that is made from calcium carbonate, the same stuff coral skeletons are composed of.

Crushed coral is another option that many people like to use. I am a huge fan and currently use it in my 120-gallon tank. Crushed coral is made of larger pieces of coral skeletons that are crushed up to form “crushed coral”.

Oolite sand is the next option. Oolite is basically fine Aragonite sand made up with tiny spheres. The term refers to the way the sand is made by using these spherical grains of sand. Oolites have to be less than 2mm in diameter. I will explain the pros and cons of each below.

How deep should the sand be in a saltwater tank?


If you are aiming to have a deep sand bed as mentioned above, you should have between 6-8 inches of sand depth. If not, then a good amount of sand is between 1.5-2 inches depth. This amount of sand looks natural and gives plenty of space for aerobic bacteria to form. Anything less than 1.5 inches of sand can look bare and be blown around the tank easily with your pumps and make a huge mess. Not to mention the fact that sand can cover corals causing them to suffer and even die.

Marine Depot Aquarium Supplies

Things to consider when choosing a substrate


What is your objective for using sand, crushed coral, or oolite? Is it just for aesthetic reasons? If so, then you need to consider how fine the sand is and the color. You can choose white, beige, pink, even black sand is popular.

Are you looking for a deep sand bed? If so, remember you will need 6-8″ of sand which costs more than a regular sand bed.

Do you have or plan to have a sand sifting fish or invertebrates? If so, then crushed coral will be out of the question for you.

How much water movement or flow do you plan to have? If you are keeping SPS corals or want to have plenty of flow in the tank, then you may not want to use a fine thin layer of sand as it will just be blown around.

You will need to calculate how much sand you will need to make your desired depth. For example, let’s say you want to have a 2″ sand bed for your 50-gallon tank. How much should you buy? Like when choosing the amount of rock for your tank, a general rule of thumb is 1 pound of sand per 1 gallon tank size. So 50 pounds of sand is what you should aim for. You can use an online calculator to help figure out the amount you need.

Depending on how you plan to aquascape your tank, you may prefer a sand base over a crushed coral base.

Best substrates for saltwater tanks


  • Aragonite sand
  • Crushed coral
  • Oolite


#1. CaribSea Arag-Alive Special Grade Reef Sand


Special grade reef sand with a grain size of 1-2mm. Live sand that contains the broad and selected strains of marine bacteria. This helps create a natural biological balance and reduces cycling time.

This is coarse sand made with 100% Aragonite for use in shallow or deep sand beds. This sand will arrive wet to preserve the life of the bacteria in the bag.


#2. CaribSea Arag-Alive Fiji Pink Sand


Another great product from CaribSea and is a personal favorite of mine. The Fiji Pink reef sand is 100% Aragonite that is good for shallow or deep sand beds. It has a grain size of 0.5-1.5mm. It also is live sand that contains the broad and selected strains of marine bacteria.

This helps create a natural biological balance and reduces cycling time. This sand is a soft pink color, but don’t think of it as completely pink. It has some pink flecks in it and the sand is mostly white and very natural looking. Sand sifting fish and inverts will love digging in this sand.



#3. CaribSea Florida Crushed Coral, Geo-Marine Formula Sand


If you are looking for something that is coarse for a shallow bed, then crushed coral is for you. The CaribSea Florida crushed coral contains aragonite which provides up to 25 times the buffering power of other crushed corals. It is great for establishing and maintaining your tank’s PH level and provides maximum surface area for water purifying bacteria.

This crushed coral is a 2-5mm grain size and can increase your bioload by up to 55%.



#4. CaribSea Ocean Direct Live Sand Oolite


Oolite is very fine sand with grains of 0.25-1mm. It is calcium carbonate (Aragonite) made up of tiny egg stone (ooids) and can be no larger than 2mm. Oolite is a very natural looking sand and is an effective substrate for creating a natural environment for a reef tank. Great for shallow and deep sand beds.

CaribSea Oolite sand is made with no additional chemicals or special processing. It uses a patent-pending Sea Breathe laser technology which preserves real live sand with its own original bacteria. One thing to note with Oolite is the fact that it can be composed of Phosphate and Iron minerals. Just make sure you buy this sand from a reputable source like CaribSea to avoid this.




In conclusion, when choosing a substrate for your saltwater tank, there are a few main things to consider. Of course, you most likely want something natural looking which all of the items mentioned above will make for an awesome looking sand base. If you have sand sifters, make sure to buy something fine. If you have lots of water movement, make sure to buy something coarse.

A deep sand bed requires fine sand, so keep that in mind. Also, calculate how much sand you will need. The general rule of 1 pound per gallon will give you about 2″ sand depth in your tank. But that will depend on the tank dimensions. You can use the online calculator to check your tank.

Any one of the mentioned sands above makes for a great substrate and you will be happy with whichever one you choose!


Thanks for reading!