Hey,
I have the same unit... Don't use the Sedra 5000 pump as it isn't powerful enough, as I had tried.
But I found the needlewheel impeller from it, is almost exactly the same, so I put that into the original GX-4100 pump and it works flawlessly.
Now if you need impellers, Dennis @ Gold's in Calgary has 2... He will probably give you a good deal, as I won't take them anymore, as I now don't have that skimmer in use.
Hope this helps.
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Setup: 180G DT, 105G Refuge (approx. 300lbs LR, 150lbs Aragonite)
Hardware: Super Reef Octopus SSS-3000, Tunze ATO, Mag 18 return, 2x MP40W, 2X Koralia 4's Wavemaker
Lighting: 5ft Hamilton Belize Sun (2x250W MH, 2X80W T5HO)
Type of Aquarium: mixed reef (SPS & LPS) with fish
Dosing: Mg, Ca, Alk
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