I have this thermostat on my rack system. I have seperate heat strips for each tub and each heat strip has it's own plug. All of the plugs are plugged into a power strip and the power strip is plugged into the hydrofarm. The herpstat comes with one temp sensor probe. The probe is attached to one of the heatstrips and when that heatstrip reaches the desired temp, the hydrofarm kills the power to the powerstrip which kills the power to all of the heatstrips. Once the probe recognizes that the temp has dropped a few degrees, the hydrofarm repowers the powerstrip and the heat strips. This works well because all of my heatstrips are identical and I want the temps in each tub to be identical.

Basically if you used the thermostat, your light would cut off each time the desired temp was reached on the UTH...so basically it would cut on and off every 5 seconds or so.

What is the purpose of the black light on your tank? Extra warmth? The UTH should be enough. You could plug the light in seperately if you want it on all the time.