I was interested to see this video, as he employs a cooling sink which run the liquid straight over the thermocouple. I thought that this would be a better way of cooling, although then you would be running your nutes through this all the time (not necessarily a bad thing).
I was surprised that his temps don't go much cooler than 20C. I got my res down to 18C within just over an hour... And this was using the fan in the opposite direction. Mine extracts the cool air through the bigger fins and blows it onto the res, and uses the smaller heatsink to dissipate the heat.
I didn't use thermal paste though! I have ordered some, and a 2nd thermocouple to add to my little setup, so will let you know how much more effective it is with a 2nd thermocouple and some cooling paste...