Robin here! I decided to write a list of everything you should originally get for the perfect hermit crab setup and why it's important. It's crucial to know that hermit crabs need a lot more commitment, time, and finance than many other pets. They aren't as simple and short lived as pet stores make them seem. Let's get started with the checklist!
1. A glass terrarium
Your tank should be at least 10 gallons.
2. A lid for your tank
This is especially important if you have other pets or if your hermies have a way to escape, but even if they don't you should have a lid. A third or a half of the tank lid should be covered with plastic wrap to keep the humidity in.
3. A temperature/humidity gauge
This is very important so you know the exact temperature and humidity in your crabitat at any given time.
4. A heat source
Hermit crabs require a temperature of 70-80 degrees in their tank. 75 degrees Fahrenheit and 78 Fahrenheit are the ideal temperatures. I use a reptile under tank heater (UTH) but with crabs do NOT use it under the tank! Hermit crabs burrow and occasionally molt, and this can be dangerous. Place the heater on the side of your tank just above the substrate. I have two heaters, as one of them doesn't work too well. It's not a good idea to use a heat lamp, as these could dry out your hermit crabs' skin.
Never buy the pelleted food pet stores offer you. Feed your hermit crabs a variety of fresh fruits, vegetables, and other crab safe foods. You can find lists of what's safe for hermies online. I have made homemade recipes for my crabs, but the food I'd recommend the most are the homemade, natural, healthy foods on the Hermit Crab Patch website. Be sure to Google their online hermit crab supply store for their inexpensive but quality foods!
6. Freshwater & Saltwater
Hermit crabs require both freshwater and saltwater in their tank, and it should be available to them at all times. The crabs should be able to fully submerge in both waters while still able to easily climb in and out of the bowls. Some people with use sponges, reptile ladders, bird ladders, or other objects for their crabs to get in and out of their freshwater and saltwater.
You need bowls for your crabs' food, freshwater, and saltwater! You don't need anything fancy for a food bowl. I've had most success using large bottle caps and small reptile bowls. For freshwater and saltwater, it should be deep enough that your crab can fully submerge in the water and is spacious enough for your crabs to walk around in it.
You need substrate for your crab tank! I personally use play sand, but some people will use coconut fiber or a mix of sand and coconut fiber. Personally, I feel sand is the best option but there are other wonderful options out there as well. Make sure the substrate is inches high so your crabs can comfortably bury and have room to properly molt. It's also important that your sand is sand castle consistency so it's easiest for your crabs to bury.
Your hermies need extra shells to change into when they grow and/or when they get bored of their current shell. NEVER EVER use painted shells! I don't care how cool they might look or if they're painted with non-toxic paint...they still could have stickers, paint, or sharp edges inside, and even non-toxic paint contains chemicals that could harm your crab. It's always a good idea to have plenty of natural shells in your tank. Have some slightly larger than your crabs, some slightly smaller than your crabs, shells that perfectly fit your crab, and shells of all different sizes and varieties in your tank. As with many other crab accessories, clean new shells with boiling water before giving them to your hermit crabs.
10. Hides & Climbing
For the comfort of your hermit crabs, provide them with dark places to hide and rest like coconut huts, crab shacks, caves, etc. Your crabs should also have places to climb to keep themselves busy, fit, and mentally stimulated. Cholla wood, vines, crab-safe branches...they'd all make great crab climbing items!
I hope I didn't leave anything out!