I use the aqualogic 1/3HP on my 240 Gallon, but there's a lot of choices - goto google.com and search on aquarium chiller and you will see what I mean - custom sealife is another good one and IMHO a great company to do business with.
I have a 1/3 HP CSL on my 150 it work great. Very quiet and not huge like some chillers can be. Check ebay also, I picked mine up for $620 brand new with the controller. It was about $100 cheaper than MO places.
I have the cyclone coil chiller. It dropped my water temp in my 75 3 degrees in one hour. For your tank a 1/3 horsepower would be more than enough. I use a 1/5th hp.
