HCA: Hermit Crab Association

Hi, we recently purchased a pre set up crabitat with 3 hermit crabs, and I have some questions.

1. It was suggested that we purchase reverse osmosis water. We use the reverse osmosis waster as their fresh water and add Aquarium salt to it for their salt water. We recently purchased a mister (we haven't added it to the terrarium yet). The mister does not work with the reverse osmosis water. What should I be using in the mister instead? Dechlorinated tap water? Salt water?
2. We added some plastic to the top of the terrarium (previously mesh) so our humidity levels are now under control. Our heat seems really low. The guy at the petstore said that humidity is the most important factor and said not to worry about our heat. We live in Calgary, so rely on our furnace in the winter, we heat our house to 70 degrees F in the day and 65 degrees in the night. We have an UTH, but the heat in the terrarium is usually around the 70 degrees mark. The crabs are burrowing for most of the day, and I assume it is because they are not warm enough and are going down where it is warmer. We recently purchased a new thermometer and hygrometer, so once that is installed we can make sure the temperatures are accurate. Should we be measuring the air temperature or the temperature under the substrate? Should we be adding a heat light? The UTH is currently under the tank, should it be moved to the side?

Def need to move the heater to the side of the tank - temp needs to be closer to 80.

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Unfortunately most pet store associates know nothing about hermit crabs. As amandapri82 said, the heat should be closer to 80. The uth goes on the outside back or side of the tank. Best bet is to cover the entire back from top of the substrate up. Heat lamps will zap the humidity. You can insulate the tank around the heater unless it's the Ultratherm brand, which isn't sold in stores but is very effective. It's the air temp you want to measure. How deep is your substrate? Is it sandcastle consistancy? What are you using for substrate? Crabs like to bury during the day since they are mostly nocturnal. I never heard of reverse osmosis water. But I've only been at this for a year. You should use Prime to dechlorinate your fresh and salt water. It removes chlorine, chloramines, heavy metals and neutralizes ammonia. And add Instant Ocean for the salt. It's a marine salt which they need, not aquarium salt. And be careful with misters. They can flood the tank. Using bubblers in the pools really helps with the humidity.

I’m not sure why the mister’s not working. Perhaps a faulty mister? RO water is safe, but conditioned tap water is more commonly used because it’s cheaper.

Yes, the UTH should be on the side. Having six inches of sand (or more) on top of it won’t be advantageous.


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RO should work with the mister as it's nearly the same composition as distilled, which is cheaper and therefore normally recommended more. The idea is to use water free of minerals to keep the mister from getting scale buildup, and the enclosure from getting water spots.

If you are using RO for their water, using a marine salt mix becomes important. This is a product for saltwater fish, like Instant Ocean. Freshwater aquarium salt will not cut it - it has one element while marine salt has over 70. Land animals have adapted to getting needed minerals from their fresh drinking water and RO has none. It has to be made up for in some way, and it's why treated tap water is almost always the better choice for hermits. RO systems are only recommended for saltwater fish tanks where mineral composition needs to be known and exact, or for some softwater freshwater species though it also needs additives to put some minerals back in.

You want to measure the air in the tank. For Purple Pinchers, anything over 72 is fine, but you'll see more activity around 80. Temperature is just as important as humidity, if not more so, as they are tropical animals and cold weather is foreign to them. Like the others have said, warm the air, not the bottom of the substrate. You won'y see much temp change with it underneath, and it's also a fire hazard when trapped under all that substrate. (They are designed to work with 1/2 inch or less for reptiles.)

So if we just use tap water with water conditioner that is preferred over RO water? Our current conditioner is "crabworks water conditioner" and says it "removes harmful chlorine, neutralizes heavy metals". Is that good, or should I get something different?

Our substrate is dark sand and moss, not sure of types because it was in the terrarium when we bought it from the previous owners. The substrate is about 3 inches in most parts, 2 inches where low and 5 inches where there is a little hill.