HCA: Hermit Crab Association

I recently got 5 crabs. 2 are very small, 2 are medium and 1 is pretty big. I have a bunch of shells that I need to put in the tank but other than that is there anything I should be doing differently? The substrate is 5:1 sand and eco earth, about 6 inches deep. It's a 29gal tank. I have some plastic wrap on the top of the lid for moisture. I need recommendations for what I should use to heat it.. are lights beneficial?
Here are the photos of the tank
https://imgur.com/gallery/JmBO9Mt

edit- I don't mind what I need to buy

Heat lamps are legitimate but can’t be used at night. A heat mat on the side of the tank would be easier to use than either a lamp or ceramic emitter (Bean Farm and Fluker’s both have good ultratherms).

Otherwise I would definitely recommend adding some foliage and other decorations. Hermit crabs are more comfortable if they have cover.


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