o.k. there's several ways you can do this...
the cheapest is to just order the regular sedra 2500 pump, and to just switch over the volute,venturi, and needlewheel from the resun into the sedra. then there's a little plastic fitting that screws into the outlet of the pump that attaches it to the wall inside the skimmer.
now, if you get the skimmer pump version, you wont be able to screw that little plastic fitting into the pump outlet, because sedra glues a plastic outlet into the screw threads. like me, you would have to dremel out that outlet and hope there is enough thread beneath it to grab the screw in plastic outlet from the resun. so for this reason alone, i suggest getting the regular sedra 2500. if you want more power from the skimmer, then yes, the sedra needle wheel and venturi are better than the octopus ones on the resun, and you could buy them seperately, but a mesh modded impellar from the resun actually is as good as the sedra nw. it's the venturi that is a big deal...but again i say, if your happy with the power of the skimmer and you just want a reliable, quiet pump than just switch the resun out. the aqualifter is perfect for keeping the pump cool as well, just drill a little hole in the pump back plate (dont drill through the epoxy seal!!! just the back plate) and put the little water/air hose in the hole. then just stick the aqualifter on the top of the skimmer, allowing it to suck water from the skimmer body and deliver it to the hole in the back of the sedra.there are little slits in the baclkplate of the sedra pump that the delivered water will escape from, all the while keeping it cool.
if you dont do this, your sedra pump WILL overheat!! it's the design of the skimmer, and how the motor block stays unsubmerged, and doesnt get water cooled the way it's suppose to:idea: