HCA: Hermit Crab Association

Does anyone know what the lower range of temperature is survivable for a purple pincher?At what temperature do they start getting stressed?

My understanding is 75 is the minimum. They have survived colder but it is not good for them.

Thanks.I've got one tank on the floor. No matter how much I heat up the room, the heat rises and it stays cool.I've been meaning to move it next to the other tank anyway.