I am buying a hermit crab from the PetCo store, but I do not wish to purchase an under-tank heater. Is there an alternative to keep the tank warm?
An overhead reflector light or ceramic heat emitter can serve as an inexpensive source of heat over a tank. Some may even say a preferable source of heat since it more accurately mimics the warming effects of the sun. Not only that, but with an overhead spot source of radiant heat, you can place it on one side of the cage so the crab will be able to freely move closer or farther way to regulate how much warmth they need throughout the day.
Use a thermometer to determine that the range of temperatures inside the cage is what the crab needs. And if you are using a standard light bulb, be sure you turn it off at night (while assuring that the temperatures do not drop too low).