Good luck with the Skimz products. I run two (2) SM251's and a SM121 on my tanks. In the two years I have owned them, I have replaced all the pumps at least once. The impeller's will also swell, crack and sieze up. Some of these failures were covered under warranty, some not.
On at least three occassions, the cords on the pumps have leaked enough electricity that I have been shocked. These pumps were replaced by the retailer.
I would have jettissoned these POS's a long time ago, but they are the only skimemrs that will fit in my sump under my 250G DD's.
Caveat emptor.