Help with leopard gecko heat lamp!?

I rescued a leopard gecko yesterday that I was told is about 10 years old. I bought it a heat lamp and put a daylight basking light in there. I was told to get a 75 watt, so I did. It didn't seem to heat up the 20 gallon Long terrarium she was in. I was cleaning the terrarium and it broke so I am borrowing a 30 gal (I think) aquarium from a friend until I can get another terrarium. The 75 watt definitely isn't heating up the terrarium enough. What wattage does the light bulb need to be? And should I get a red light bulb for at night, or will she be okay without the light on at night? I was told that an undertank heater was a bad idea because they tend to fall asleep on them and burn themselves. So somepne with experience, PLEASE tell me what kind of lights, etc I need for an adult leo being housed in a 30 gallon aquarium. Also, she may eventually be downsized to another 20, so what would I need for that size also? Thanks!