Good choice on the skimmer! I have an rs80, and it is my ONLY filter. It keeps the water perfectly pristine, and clear. I only have 1/4 inch of clearance from the collection cup, and the bottom of the tank. Luckily, the 100 is actually 2 inches shorter than the 80, so you wont have to worry about that. The next step up from the 100, the 135, will not clear the underside of the tank. So don't go bigger than the 100. You will definatly be cleaning the collection cup with some NASTY skimmate. The nastier, the better! lol.