Does anyone know anything about keeping hermit crabs?

To live comfortably in captivity, Hermit Crabs need the following as basics:

Constant temperature of about 72 degrees Farenheit. Cold temperatures will kill them, as will putting them on a sill to bake in the sun! Signs of a Hermit Crab overheating is a musty smell and a brown colored discharge.

Constant humidity level of at least 70%- it's environment should be moist and "tropical".

Food, water, shells and other decorations to stop your crab from getting bored.



HTH.

Here are some essential tips on how to keep your hermit crabs happy and healthy.

You have to provide them a glass aquarium -- at least a 5 gallon for one crab and 10 gallons or more for multiple crabs. Get a lid for the top and try to keep a minimum humidity of 70% and a minimum temperature of 72 degrees Fahrenheit as adrian says.
You will also need an under tank heater for your crab's aquarium and invest in a thermometer and humidity gauge to monitor the environment and make changes as needed.
Get 1 to 2 inches of play sand in your hermit crab's home and remember to keep it slightly moistened at all times.
A fresh bowl of non--chlorinated water daily is vital.You can purchase dechlorination drops at your local pet store.
You should buy a wide variety of shapes and sizes of shells for your crab to change into as desired. Hermit crabs molt and grow on a regular basis and need larger shells to accommodate them.
In addition to a good staple hermit crab food (available in most pet stores), provide them with a variety of other foods. They also enjoy fresh apples, bananas, peanut butter and a variety of other foods.
Hermit crabs love to climb and play, so provide a variety of toys such as driftwood, flower pots, shells and fish nets.

Hope you and your Hermit crab have fun together.

How big can they grow?

Do they need to be on salt water?

They don’t need salt water just sand and an aquarium. As long as their home is humid, your hermit crab would survive. I think they can only grow 2-3 inches.

Just for 2-3 inches. So, I can get at least 5 hermit crab in an aquarium?