redearslider.com

For a 55gal aquarium is the PowerSun UV Bulb 100 W adequate to provide a comfortable basking temp? Or will I need two?

This bulb give off a lot of heat, and I think it would be sufficient for a 55-gallon--you want your turtle have a gradient of temperature, so that he can regulate his body temp. Look at what the instructions are for the correct distance from your turtle--you don't want to cook him. A basking area temp of high 80s - 90F is good.