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Substrate - It's Importance & How To Make It

Updated: Sep 24, 2023

In the wild, Hermit Crabs burrow deep down into the sand dunes to safely moult.

Now that they have been brought into captivity, we must provide them with a similar environment and substrate so that they can continue to safely moult and survive.

What is Substrate?

When people refer to substrate (sub) in the Hermit Crab world, we are referring to the sand mixture at the bottom of the tank.

Substrate is a vitally important aspect of a Hermit crab tank and can often mean life or death for Captive Hermit Crabs.

Too shallow and they will be forced to surface moult, too inconsistent and they won't be able to tunnel, too dry and their moult caves will collapse, too wet and they could drown, wrong products used and they could die.

Building the right substrate may sound scary and hard, but it is actually very easy, and if done right, it only needs to be done once.

Why is deep substrate so important

In the wild, Hermit Crabs can dig down 12+ inches (30cm) into the sand to begin their moult. They need a dark environment for their moult to begin and be successful. They also need a closed off space away from predators and other Hermit Crabs to avoid being attacked while they are in such a vulnerable state.

If you don't offer deep substrate for a Hermit Crab to moult in captivity, they will likely be forced into a surface moult which is very unnatural for them and can often lead to death or complications such as limb loss.

Products needed to make your substrate

You will need the following supplies to build your substrate

• Coir Peat Brick

• Playsand

• Prime Water Conditioner

• Water

• A bucket or Scoop for measuring

• 2 x Large Bucket or Tub

What ratio of substrate do Australian Hermit Crabs need

In Australia, we try to make our substrate as close as possible to what they have in the wild. The best way to do this is by making your subrate a ratio of 8 parts sand to 1 part of damp coir peat.

This is very easy to measure if you are not usually comfortable with ratios.

Simply use your bucket or scoop and fill it 8 times with sand, and then 1 time with damp coir peat. Repeat the process until you reach the desired level.

Hermit Crab species overseas will often use the 5:1 ratio of 5 parts sand to 1 part coir peat. Our natural environment over here is abit more sandy, more of an 8:1 ratio, which is why our ratio is different for Australian Hermit Crabs compared to their overseas cousins.

How deep and why

Because Hermit crabs prefer to dig down deep to complete their moults, it is recommended to have a MINIMUM of 6 inches (15cm) of substrate. However, if you can go deeper, you should.

Setting up the substrate

• Fill a large bucket or tub with tape water and treat it with your Prime water conditioner. Break apart your coir peat brick and soak it in the water until completely soaked, making sure to break it apart so there are no dry parts left.

• Grab yourself another bucket or tub and scoop up the sand with your desired measuring device 8 times and place it into the bucket.

• Remove some of the soaked coir peat and wring it out in your hands until it is damp (not soaking wet) and measure out 1 part (this should be the same device you used to measure the sand) place it into the tub that has the sand in it. Continue with the 8 scoops of sand and 1 scoop of coir peat until you have a large mixture in the bucket.

• Using your hands, thoroughly mix the sand and coir peat together until it is completely combined. Place it into your tank, and continue the measuring/mixing process until you have completely covered the bottom of the tank and have the sand mixture sitting at a minimum of 15cm.

Keep in mind that your substrate will settle over time, so going abit over 15cm is best.

Use a ruler or tape measure to check the depth, the substrate should be equal in height throughout the tank. There is no need to have a shallow side and deep side.

By having the entire substrate the same depth, you are offering more moulting space for your crabs.

Substrate Consistency

Your substrate should be a sand castle consistency at all times. What does this mean? If you scoop up some substrate and firmly squish it into a ball, it should keep its shape (like a sandcastle)

You can also check the consistency by poking a finger into the substrate or pushing a straw down to the bottom of the tank up against the glass and removing it. The holes you make should keep their shape. The substrate should not look wet, only moist.

Inappropriate Substrates

Under no circumstances should these products be used as substrate.

They do not allow your Hermit Crab to dig down and safely moult. They won't hold their moisture content and will not allow a safe cave to be built. When these products are used as a substrate it is highly likely that your Hermit Crab will either surface moult, drop its shell due to stress or pass away.

Unfortunately, pet stores will market these kinds of substrates as appropriate. They do not know any better, and majority of pet stores are forced to market their crabs this way.

By not providing the correct substrate mixture, your tank will lack in moisture and become dry, your crabs will also become stressed with a lack of safe spaces to moult and distress.

Although they may come across some of these types of substrates in the wild, they are not the substrates that a wild Hermit Crab chooses to moult in.

We see alot of people claim they have had their Hermit Crabs for 6+ months on these types of substrates and they are doing just fine. The truth is, they are not. They are in desperate need of a moult and will be lacking in growth due to not having a safe opportunity to moult, they will usually be forced into an unnatural surface moult or death within a year. If these products are your current substrate, it is not too late to fix the issue and create a safe and appropriate substrate for your crabbies.

• Tanbark

• Calcium Sand

• Reptile Bedding

• Dirt

• Just Sand

• Just Coir Peat

• Coconut Fibre

• Rocks and Pebbles

• Coloured Sand

• Shell Grit

• Reptile Sand

Substrate - not just for moulting!

A lot of people think substrate is only for moulting, but that's not true at all.

Substrate plays a much bigger part within your Hermit Crabs world.

They will often dig down into the substrate to distress when they have been through a stressful ordeal such as being purchased from the pet shop, moving homes, being handled to much, being put under stress etc.

The substrate also plays a part in your humidity and heat. By having moist substrate, it will help aid the humidity within your tank and by having deep substrate, you have less air space to heat up, making it a much more cost effective option for your electricity bill.

Hermit Crabs will also dig down into their substrate to cool down if they are feeling too hot.

Adding more substrate

Alot of owners start with the right mixture and consistency for their substrate, but make it far to shallow. There is no issues in topping up the substrate, but if you have Hermit Crabs down, you will need to be careful to not collapse their caves.

You can add 3cm of substrate on top of the current substrate every week. Adding to much will weigh down on the tunnels.

Simply sprinkle the new substrate over the top of the current one and avoid pushing down.

Why is my substrate dry

It is very normal for the top 2-3cm of substrate to dry out. This is usually caused by the heat in the air, as well as heat emitted from lights, as long as the bottom layers of your substrate are moist, this shouldn't be an issue.

Another reason for dry substrate can be because you have either placed your heat source under the tank or below the substrate line. Both of these things should be avoided at all costs. You ONLY want to heat the air, NOT the substrate.

Avoid spraying the substrate to remoisten it. This can cause a flood.

When should I change the substrate

The answer is, if done correctly the first time, never. There are only 3 reasons for changing out your substrate, a flood, a bug infestation or if you are moving house.

You can read more about substrate emergencies such as floods and bug infestations here

  • The Coir Peat Brick needed. Purchase the BLUE packaging

  • Washed playsand that is bagged

  • Coir Peat soaking in Primed water

  • Coir Peat after being broken apart and completely soaked

  • 8 parts playsand and 1 part coir peat

  • Completely mixed together and placed into the tank at 15cm deep

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Jay Badesha
Jay Badesha
Sep 25, 2023

Hey, i just wanted some advice on how to change substrate and the need to change substrate. Im confused to whether how clean it and if i should ever change it. Please help me with my further assistance to tank mantiance so i am able to have enough knowledge to take care of my hermie :)


Katrina Bucke
Katrina Bucke
Sep 21, 2023

Sooooooo helpful!!

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