Other... because I have been using a Reef Octopus SS110 in a 120 gallon mixed reef for 2 plus years. I purposely undersized the skimmer, so it would't pull pull too many nutrients out of the system, all at once. With an undersized skimmer, I didn't need to worry about its under performance, due to low nutrients, when I first set up the tank. Now that the tank is established, there are all kinds of sponges in the overflow and an established bacterial system, that take up excess nutrients without lowering my NO3 and PO4 to undetectable. Basically an undersized, but dependable, skimmer still gives me peace of mind, but a lot more control.