I recently acquired some used Power filters as backups for my 7 nitrate filters which would need immediate replacement if one failed to flow water. However I discovered that 2 of the backups had worn impeller shafts:shakehead:. So the idea was I had to replace them by brand but how to do so on the cheap with the above mentioned brands. Not a very cost effective proposition so I had to study the problem and what I discovered after some research and test swapping of working parts was that all 3 name brands PF's mentioned above use the exact same motors, magnets, shafts, coupler, and impeller housing diameter and depth, are all swap compatible. The only difference is the impeller size and shape itself which determines GPH, the Penguin 350 having the largest impeller and therefore largest GPH. Having said all that what this means and what I verified in swap-testing parts and research is that any combination of these parts mentioned will fit and operate in any of these 3 PF's perfectly. This is important to know because prices ($10-$18) and availability (hard to find) for these parts very greatly. So FYI, I was able to find new Whisper 60 impellers for $5.49 each with free shipping at Pet Mountain.
http://www.petmountain.com/product/...ed-pf-30-60-triad-3000-impeller-assembly.html
http://www.petmountain.com/product/...ed-pf-30-60-triad-3000-impeller-assembly.html