Crabitat: Substrate - Products, Mixing, Maintaining & Problems

This is where you discuss the conditions of your crabitat -- temperature, humidity, substrate, decorating, etc.
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Crabitat: Substrate - Products, Mixing, Maintaining & Problems

Post by HCADirectors » Wed Mar 13, 2013 2:06 pm


Why is picking the right substrate important?

Substrate is extremely important for hermit crabs because of their need to be able to dig and stay underground for months at a time to safely molt. Molting problems are the number one health issue that hermit crabs face, so offering a proper substrate can do a lot to keep them happy and healthy for a very long time. As with most hermit crab products, sand sold specifically for hermit crabs is not safe for them. Read on to find out why!

How much do I need?

At the very least, you need it to be three times as deep as your biggest crab stands tall. This will allow the hermit crab to be able to get fully underground safely. However – more is better! When you have multiple crabs they will dig a lot, and they prefer to have a lot of substrate on top of them for safety when they molt. In order for the caves to not collapse, and for multiple hermits not to accidentally come across each other underground, three times or more is recommended. Some species, such as straws and Es, will be ecstatically happy with 10 or 12 inches of substrate, regardless of the crabs’ sizes.

We have a chart that recommends tank size and substrate depth. There is a full article called "Tank Size, Crab Size & How Many Can You Have?" located >here<.


Why does it need to be kept moist?

Substrate should always be kept moist enough for a hermit crab to be able to dig underground and form a small cave. It needs to be damp enough that it holds its shape when you squeeze, but not so wet that it drips or pools water. (We call that “sandcastle consistency”.) Too dry and it’s not diggable, too wet and you risk bacterial growth and flooding at the very bottom of the tank.

Which water to mix and rewet with?

Substrate can be made using saltwater that is the same mix as their drinking water, in order to keep everything fresh, and cut down on the risk of mold and mildew growth. The choice to use freshwater or saltwater is up to the individual keeper.

The substrate may also require maintenance such as spraying with dechlorinated water on a regular basis in order to keep it moist enough, since the moisture in it will evaporate over time. Use freshwater to spray if saltwater has been used in the substrate, as salt does not evaporate. Spraying constantly with saltwater can lead to a harmful salt build-up!

Water should be dechlorinated when mixing substrate, but it's not as harmful if untreated water is used accidentally. Problems have never been noted when it has happened in the past.

Sand and Cocofiber - ideal substrates

Playsand and cocofiber are the two things that are regarded as completely hermit crab safe. They can be used by themselves, or mixed together for the best of both worlds. Many crabbers prefer a mixture of 5:1, which means that for every 5 parts of sand, 1 part of cocofiber is used. A mix can be easier to keep at the right level of moisture, and is highly recommended for newer crabbers.

Sand is roughly 10 pounds to fill one gallon of space.
Cocofiber is roughly 1 brick to fill one gallon space.

Playsand is cheap - less than $4 for 50 pounds, which is enough for a 10 gallon - and very easy to find at any home improvement store. Because it has been cleaned, sterilized and screened already, most owners will use it straight from the bag as-is with no extra washing or baking. Sand is sold in the same place as cement. It holds its shape very well when made sandcastle consistency, and generally stays moist for a long time. Pool Filter Sand is the same thing as Playsand, except it has been screened to a uniform size and should contain less dust. Playsand is made of ground silica.

Sakrete Playsand
Quiktrete Playsand
Pool Filter Sand

All purpose sand is another option. It has a bit more course grain size than playsand, and holds molting caves very well. It also tends to stay moist better than play sand. It has not been washed or screened, and it has a heavier clay content, so any rinsing should be done outdoors. Many hermit crab owners use it straight from the bag, though.

Quickrete All Purpose Sand
Sakrete All Purpose Sand

Dry aragonite sand has been used successfully by some crabbers rather than using playsand. However, aragonite sand is calcium carbonate, which means it can possibly develop the same problems as calcium sand (see below) due to its porous nature, and should be watched closely if used. It is larger grained than calcium sand and it will not clump or harden.

Kolorscape Playsand (Part aragonite, part silica)
Carib Sea Aragonite
Nature’s Ocean
Seachem Meridian

Cocofiber is coconut husk that has been processed to be as fine as coffee grounds. It can be bought loose in a bag or compressed in a brick that you expand using water, and can be found at any pet store. The compressed bricks have an easier time if you use hot water, and you might want to use less than the directions state so that the cocofiber isn’t dripping wet once it’s ready. Cocofiber can be difficult to get to the right moisture level, and it should be kept on the dryer side rather than the wetter side so it doesn’t get funky over time. Cocofiber will boost the humidity level or solve most humidity problems you may have in your tank.

Make sure to buy the finer type of ground cocofiber as it is ideal for hermit crabs to dig in. The bark, fiber or chip kind are hermit crab safe and can be used to add some texture and variety to another substrate, but by themselves they are just too chunky to allow the crabs to form the caves needed for molting.

EcoEarth (compressed brick & loose) by ZooMed
Hermit Crab Soil (compressed) by ZooMed
Plantation Soil (compressed) from Exo Terra
Plantation Soil (loose) by Exo Terra
Forest Bed by T-Rex

Safe Commercially Sold Substrates

Hermit Crab Patch has been selling their pre-made hermit crab sand mixture for nearly two decades via mail order. While expensive, it is a safe option that has helped many hermit crab owners over the years, especially those with mobility issues.

In 2015, Fluker's Farms came out with a pre-mixed hermit crab substrate that is made using playsand, coco fiber and sea salt. While more expensive than making the mix yourself, their pre-made mix is completely safe for hermit crabs and is the same recipe that most crabbers have been recommending for years. It is called Hermit Beach Sand Substrate for Hermit Crabs.

Troubleshooting Problems

Mold is unfortunately rather inevitable in a crab tank - between the stagnant air, high humidity, and organic matter from food and cocofiber, mold has the perfect conditions to grow. Many times, hairy growths on the substrate is coming from leftover food and can simply be scooped away, solving the problem. If it keeps coming back, a small amount of saltwater spray usually solves the issues for good. For tanks that have recurrent mold issues, the humidity may be too high, or there may be a need for better air flow.

The dreaded flood occurs when too much moisture has been introduced into the enclosure, causing water to sink and pool down at the very bottom. If caught early, excess water can be absorbed using paper towels or dry/unexpanded cocofiber with very little harm done. It's not just overspraying the substrated or spilling bowls that can cause a flood - humidifiers and foggers, high humidity, and just a slow buildup from all sources of water over time can be the cause.

Floods are physically dangerous to molting crabs, as they can become stuck underwater while in their vulnerable state and drown, or have their caves collapse from the water. If a flood occurs with molters down, making sure they are safe is a priority and is pretty much the only time that hermit crab keepers agree that it is safer to dig them out, than to wait it out.

Floods can be checked for by observing the bottom of the tank, or by sliding a stick or knife down the front of the glass and gently creating a small shaft to check for standing water.

Bacterial Bloom
If the water from a flood has been sitting for even a short period of time, the lack of oxygen and darkness can cause what is known as a bacterial bloom. These can also form any time the substrate has been oversaturated - even if there is no standing water present. Severely compacted substrate can also form bacterial blooms. In rare cases, small isolated blooms can form from buried food or dead hermit crabs.

Bacterial blooms are serious. The bacteria that creates them, also creates acidic conditions that are dangerous and gases that are toxic. Affected substrate will be darker in color, usually grey, and will smell strongly, usually of rotten eggs. These areas should be removed and discarded - but the rest of the unaffected sand is safe to continue using.

Fluffy, aerated substrate is both the cure and preventative for bacterial blooms.

Drying Out
Dry substrate is also a serious issue, as it severly endangers molting crabs, and drops the humidity levels in the tank. The best possibility is that all your hermit crabs are above ground, which means you can remove them and the decor, and can start over by re-wetting the entire mass of substrate.

In reality, the timing almost never works out that well. There are a few options for re-wetting slowly and safely with crabs underground. Flooding is a real risk when not mixing the substrate up, so always keep track of how much water you are adding, and wait to see if it pools at the bottom before adding more.

Spraying - Go slow, evenly wet the surface, and wait 12 to 24 hours for the water to absorb before deciding if it needs more. For larger tanks, pump sprayers can be wonderful tools!

Pouring - If you cannot see any molting crabs at the very bottom of the tank, choose a corner and slowly add in water so it sinks to the bottom. Wait a day, and the substrate should moisten from the bottom up with no standing water. This method rarely gets the surface level back to sandcastle consistancy, and flooding is a greater concern.

Humidifier/Fogger - this has the same effect as spraying, but at a much slower pace, so that the substrate has a better chance of absorbing the water evenly. Again, monitor how much water is being added in, and go slow to prevent flooding.

If the substrate continues to dry out quickly, there may be other concerns in the tank, such as too much airflow or an outside environment that is too dry. Please check our Humidity FAQ for ideas, located >here<.

What substrates shouldn’t be used?

Hermit crab sands and reptile sands are actually a very fine calcium sand. While this may sound helpful, the sand used by itself is dangerous. This type of sand cannot be kept moist without a large risk of it developing bacterial growth, and as it starts to dry it can harden like a rock and trap or harm hermit crabs. Even when wet it clings to hermit crabs and causes them discomfort. Most of these sands have also been dyed, which can stain a hermit crab until the following molt. While this sand should never ever be used by itself, some crab keepers have reported success with using a bit mixed in with cocofiber or regular playsand.

Gravel of any size isn’t safe to use since hermit crabs can’t dig or make caves. It can be used as a decorative accent in the tank to keep messes down around water bowls, but it will eventually get mixed into the rest of the substrate. (This won’t hurt the hermit crabs, but you might lose the effect you were going for.) It should never be used as a primary substrate!

Coral or crushed shell is too rough and too sharp to be used on its own. A small amount can however be mixed into cocofiber or sand as an easy calcium snack for both hermit crabs above ground and those that are molting.

"Live Sand" sold for marine fish tanks is aragonite sand that contains bacteria and microorganisms, and is sold wet. Aside from being drastically overpriced for use in a hermit crab tank, the organisms in the wet sand will start to rot if not used in a cycled aquarium (in water), and therefore this type of sand should be avoided.

While moss is a great thing to have in a hermit tank, it should not be used as a primary substrate as it does not offer any protection for them while molting.
Last edited by wodesorel on Mon Aug 07, 2017 9:55 am, edited 1 time in total.