Heating a 55 gallon tank

Question
QUESTION: I have a 55 gallon glass tank and not sure how to heat it.  It has two lids with lights in them but they don't seem to heat anything.  What kind of lights should I be using and wattage?  would a Under the tank heater work ?? thank you

ANSWER: Dear Molly,
thank you for your question.
An under tank heat would work, but I recommend mounting it on the sides or back of the tank. The crabs will dig down to cool off sometimes and if the heater is mounted below the tank, it gets warmer the futher they dig down.
I assume that the lights in the lid are flourescent tubes, those rarely produce any heat at all. You can use a normal household bulb for heating, but then you need to keep an eye on the humidity. I use a 100 watt bulb for my 75g, so you may want to try a 60 watt bulb, but you have to experiment a bit. It depends on how warm the room is, what substrate you use (coconut fibre bedding keeps humidity higher than sand), if you have any live plants in there ect.
I hope I was of some help to you
Jennifer

---------- FOLLOW-UP ----------

QUESTION: I have half sand and half eco-earth as my substrate.  What is your opinion on having one light a blue day light and the other one a red night light?  the lights i have now are flourescent.  Not much heat if any at all.  and are the red/ blue lights incadescent?  My humidity is doing great just can't get the temp up.  I mounted a large UTH on the back side of the tank on the sand side.  which brought the temp up to 72 degrees.  I want to thank you very much for getting back to me so soon and giving me the advice.  I just don't want to stress my little creatures when I switch them over to this big tank.  SO THANKS AGAIN!!!

Answer
Crabs actually enjoy sunbathing and bright lighting may make them more active during the day, as logn as they have enough hiding places to go to when they want to. Red or blue lights are better used during the night, the crabs cannot see red light and you can watch them without disturbing them. Blue light (the Moonglow bulbs) are also good during the night, but during the day I would use white light, a bulb you would use in a desklamp is absolutely fine for that.
Here's a very good article on crabitat lighting with examples of what to use:
http://www.crabbytalk.com/05202005/lights-and-heating/
and another one on temperature:
http://www.crabbytalk.com/09152005/the-temperature-of-the-crabitat/

If yu use a analog thermometer, it may be a good idea to cross-check the temperature with another one or a digital one, analog ones can be very inaccurate. The same is true for humidity gauges.
I hope this was helpful for you
Jennifer