I'am a seasoned hermie keeper! I have had them since I was eleven, so they are about 6 years old. Let's see.... The low down would be....
moist
sand for substrate. You can get play sand in big bags at lumber yards for around 4 bucks a bag. Make sure it is clean, and does not contain silica. Just scoop some out and dump it into their tank, (without them in it of course lol) and pour some warm water in. Knead the sand like dough until it is completely moistened. A good rule to know if it is amoist enough is to make a circle with you finger, like writing your name in the sand. If it stays in the shape, and does not cave in, it is perfect. you want it to be fluffy, not hard.
Food- I feed mine a mixture of fish flakes, crushed pellet hermit crab food, crushed coconut(with no added sugar) I also feed them freeze dried tubifex worms,freeze dried baby shrimps, and all you gotta do is mix this up and sprinkle some cuttle bone powder into it, they need extra clacium to help rebuild chitin in their skin when they molt. You can put it in a plastic peanut butter lid, or a nice little white shell you get in those decorative basketts at the dollar tree work wonderfully. (kinda white pink I think they are from scallops)
Water- Dechlorinated tap water, in a big enough dish so they can submerge most of their body. Provide some coral, or rocks, in their dish so they can climb out. A natural sea sponge is excellent for helping them out of deep dishes, helps with humididty, and they enjoy nibbling on them. DO NOT USE METAL ANYTHING in heir tanks. Hermies are allergic to metal. Use porcelein or glass, or plastic bowls and dishes. It depends on the size of crabs for the size of water dish you need. Keep their waterc elan, because they will get in and flush out their shell, getting poop and stuff in the water. Also provide them with some salt water. Do not use iodized table salt, use natural sea salt. Mix it with warm dechlorinated water dechlorination helps to disolve metals that are harmful to the critters, and chlorine burns their modified gills) taste test it before you give it to them, it should have about the same saltiness as a potatoe chip.
Humidity- Invest in a humidity gauge! I recomend ZooMed. The humididty in the enclosure needs to be anywhere from 73% to 85% or so. They like it moist, so only feed them little amounts of food they can consume in one sitting because it will mold quickly.
Temperature- They like it warm, so anywhere from 70 to 80 is perfect. And under tank heater works nicely, a heat light like for turts tends to dy out the substrate. Under tnk heaters also cause more humididty since the heat goes through the sand and evaporates the water from the bottom up.
Deco- My crabbies LOVE Cholla wood. It's like dried cactus stuff or something, Idk. But that works awesome, they love to climb it, eat it, poop on it. Take it out when you notice mold and stick it in the microwave for 45 seconds to zap the baddies. Coconut huts are great, any fish deco works. They love climbing in plastic vines with leaves, rocks, coral, shells, everything. Little plastic palm trees.
Tank- Depending on the size of crabs you have, about 1 gallon per crab is fine if they are quarter to half dollar coin sized. Any bigger then that and I would say 2 to 3 gallons per crab. I had a twenty gallon long, and it housed around 23 crabs of variou sizes.
Molting- This is a big one. It's different for every crab, but smaller ones molt more often. Molting is shedding their skin so they can grow bigger, kind of like a snake. When you notice your crab geting lethargic, haveing a grey tint to their skin, or when you pick them up and they come out of their shell, they may have a little brown or black sac behind their last pair of legs that they store food and water in. If your crab is messing a limb or a segment, they will grow a "gel" limb on the missing part. Their eyes may look cloudy. These are signs of a pre molt, and you need to Isolate them right away. A good isolation tank is a ten gallon with about 6 or 7 inches of moist sand. Again, depth depends on the size of crab. This ISO needs to be in a warm, dark place so they will not be stresed. Provide a water dish, extra shells, a hiding plac, and some food enriched with calcium. They will dig down, shed their skin, eat it, and then come back up. DO NOT DIG UP THE CRAB! If it has died during the molt, you will be able to smell it. Fishy and nasty. But if it smells a bit like chlorine, or something similar to that, they are molting. If you do not iso them, other crabs will cannabalize them.
Shells- Try to provide shells of all sizes and shapes. Murex, Turbos, Cancelleria, and ah man I cant remember the other kind. work well. Shells should have smooth insides with no cracks or protrusions, which could cause irritation to their tender little butts. try to keep them emptied of sand, so they can change and not have to get the sand out first.
welll....thats about it you can feed them anything you feed your turt, apples, melon, banana, lettuce,. I wouldnt recomend cat food or dog food because of the fat content. Try not to give them anything high in sugars or Iron/copper. If you need ANY help, you can email me at GoodApolloIVevr@aol.com
happy crabbing!