I've been messing with a ev 240 a lot. To respond to fishing guy above, I did run it on a 55 and then a 100 and then a 240. It was never too much skimmer. My corals in the 55 grew out of the tank vertically and most had to be hacked out of the tank laterally too. (I have my 240 back on the 100 gal. now.) In my experiance, its not too much skimmer except for the amount of watts it uses.
On all tanks (and with three different pumps) it does "collpase" when you touch the tank or feed it. And, it takes a good amount of time to come back up after messing with the tank. Similarly, it takes a lot of time after adjusting the skimmer (even just a slight tweak on thre valve) to see what you've really done. For me, this is just one slight negative aspect of this otherwise great skimmer.
For MatthewLaw, I've found when you have too small a pump (i.e., specifically, low of a max head pressure) you have to clean the skimmer tube often and the collection cup does not get much gunk. If you are experienceing this (alwyas skimming baby **** in the riser tube and the cuip is empty), then your skimmer is actually not working and you need to step up to a higher pressure pump. Trust me its worth it - Its like a whole new experience in skimming when an AQUA C skimmer actually skims into its collection cup and you almost never have to clean the riser tube!!! A mag 18 was too little pump for my 240, so I suspect the mag 9.5 is too small a pump (not enough head pressure) for your skimmer.