okay, how high did you turn the knob on the dimmer? I'de turn it up as high as it can go at first (obviously not under the tank) and give it about 5-10 and you should feel the heat. If it's dimming the light, it should work for the uth.

AndI've never heard of soldered the wired together. My father is an electrician, and he said that's what the wire nuts are for, no soldering required. JMO. Anyone else solder them for a dimmer?