Summarize the following:
The best enclosure to use is a glass aquarium. Size is a very important factor when deciding how many hermit crabs you will keep. A good rule of thumb is 1 inch (2.5 cm) of hermit crab per 1 gallon (3.8 l). To determine how long your crabs are, measure across the shell opening.  Remember, the habitat (or as many people call it, "crabitat") needs to be able to hold 3 dishes, climbing toys, shelters, shells, and have space for the crabs to walk around. A 10 US gal (38 l) tank usually does nicely for a maximum of 3 small hermit crabs. You may want to consider starting off with at least a 30 US gal (110 l) tank. A larger tank will allow more climbing toys and more space. Hermit crabs, when cared for properly, can live for decades and grow very slowly to the size of a baseball. The tank size will need to increase as the hermit crabs grow. Hermit crabs are escape artists. If there is any possible way for the crabs to escape, they will almost always find it. Use a secure lid to ensure no crabs escape and that all the humidity stays in the tank.  Select a lid with small air holes installed in it. If your tank has a mesh lid, you can cover it with plexiglass to prevent escapes. Hermit crabs need a humid environment, so this will also keep the moisture in the tank. Be sure to leave a little bit open at each end to allow for air flow. Hermit crabs require a deep substrate at least twice the height of your largest crab. The crabs will burrow themselves into the substrate to molt (shedding their exoskeleton to grow). You can use sand, coconut fiber, or a mixture of the two for your crabitat.  Medium crabs (golf ball size) need at least 8 inches (20 cm) of substrate for molting. Small crabs (quarter size) need 6 inches (15 cm). Tiny crabs (often called "micros", the size of a dime) need 4 inches (10 cm) of substrate. Examine the substrate carefully before putting it in the crabitat. Sift some through your fingers and check for insects. Be sure to smell it, too. Sand that smells moldy has probably been contaminated. Spray the bottom and the sides of the tank every day with dechlorinated water and keep the lid of the crabitat closed. Buy a humidity gauge at your local pet supply store and check it every day. Crabs will thrive only if the humidity is between 70-80%.  Remember that the inside of your crabitat should be like a mini-Caribbean island. It should have a moist, tropical feel to it. Keep the substrate at sandcastle consistency. You should be able to make a hole in it easily, but not get your fingers wet. Puddles of water or muddy substrate means you are misting too much. If you have a plastic crabitat with holes in the lid, place a warm moist towel over the lid to get an extra humidity boost inside. To do this, find an under tank heater or heat lamps at your local pet store. Buy a thermometer or hydrometer to measure the ambient air temperature in the tank as well.  When using a 10 US gal (38 l) tank, the best way to heat the tank is with an under the tank heater (usually referred to as a UTH). These are small pads that stick to the outside glass of the enclosure and usually raise the temperature up between 4 and 6 degrees. Try placing the unit on the bottom of the tank. Even with a thick layer of substrate the UTH will be effective. Heat lights work great on larger enclosures and can usually heat the tank to any temperature. A 40 watt light will do nicely on a 10 US gal (38 L) tank. Heat lights do dry out the tank very quickly, however, so you may have to spray the inside of the tank more often. Make sure that the heat source is placed on one side of the tank, and not in the middle. This is so the tank has a warm and cool side so the crabs can be around whatever temperature they prefer. To dechlorinate drinking water for your crabs at home, buy a small bottle of tap water conditioner in the fish section of your pet store. Follow the instructions for making 1 US gal (3.8 l) of water.  Hermit crabs cannot drink tap water. This water is treated with chlorine which can cause permanent blisters on the crabs' gills. It's a lot easier to have a batch of water ready to use for the next few weeks or so rather than having to make a small amount every day. Look for a conditioner that removes chlorine and chloramine and neutralizes heavy metals. Hermit crabs like to drag themselves into their water dish to sit and bath themselves sometimes. Be sure you use non-metallic dishes big enough for your crabs to bathe in, but not so deep that your smallest crabs will drown in them.  If you have very large and very small crabs living together, put pebbles at the bottom of the large crab’s water dish so a small crab can have a way to get out of it if it falls in by accident. Always make sure there is a way for the crabs to climb out of the dishes. Put a little bit of sponge, shells, or pebbles in the dish.  You can also make your own fresh, dechlorinated saltwater. Make 1 US gal (3.8 l) of dechlorinated water using your water conditioner. Add 10 tbsp (170 g) of aquarium salt. Let the water sit overnight so the salt dissolves. Do not use table salt to make the salt water. It contains harmful iodine. Many crabs also drink salt water prior to molting. Providing salt water allows the hermit crab to choose what kind of water it would like to drink. Use fish or reptile decor to add decoration and hiding places for the crabs. Make sure that they have large enough openings for a crab to easily enter and exit. Provide various plants and structures for the crabs to climb on.  You can use coconut huts, ceramic flower pots, large shells, reptile caves, fish decor and many other things as potential shelters. Pieces of wood, Lego structures, cork bark, fake or live plants, rocks, large coral, barnacle clusters, and fish décor all make great climbing structures. Avoid using evergreen wood in the crabitat, as it annoys the hermit crabs. Try creating a second level to the crabitat by using a shower caddy stuck to the glass walls of the tank. Fill it with moss or coconut fibre. Add a branch to act as a ladder for the crabs to climb up. Prop up a large branch into a corner and drape it with fake plants so that it acts as a tree which the hermit crab will enjoy hiding in.

Summary:
House your crabs in a large glass tank. Add a secure lid to the tank. Fill the bottom of the tank with sand or coconut fiber. Keep the humidity in the tank high by spraying the substrate regularly. Keep the crabitat between 75 °F (24 °C) and 84 °F (29 °C). Provide dechlorinated drinking water in a non-metallic dish. Set up dishes with dechlorinated freshwater and saltwater for bathing. Add decor, hiding places, and toys.