i am running a tank without a skimmer and its doing fine.. but, it has only been running for a short period of time and i can see a buildup of biomaterial in my sump... sorta a slimy film on the top.. I can definitely see the benefits of a skimmer and do plan on adding one to my tank in the future.. i suggest one (although i have no experience) and make sure you have a good skimmer.. search the board for some of the problems people have encountered with skimmers so you dont end up making the same mistakes. a skimmer will probably be the main mechanical filtration of your system so you probably want a good one...