I really wish I would have gone for the unit that held 2 filter socks. I have the Crystal 30. I feel like I am constantly having to change the single one. The sump's size was a good fit for my stand (Monterey by Marineland), leaving me room for some equipment storage under one end of the stand, but still not crowded. My Octopus Classic 150SSS Protein skimmer fit like a glove in the 2nd chamber (I believe it's to be used as a refugium there, but I don't use one of those, so no loss. If I would have had to set the skimmer up in the 1st stage of the sump, I would have had to make some drastic alterations to my overflow plumbing in order to accommodate it. Only drawback, like I said, was only being able to use the single filter sock.