Differences in GSS2 and GSS2 IMP

 I do not know if my gravity filter is a GSS2 or a GSS2 IMP so am unsure what replacement filters to order. Are the filters interchangeable? Can you use the Super Sterasyl filter candle in either model?

The filters are interchangeable. The IMP filters have a CN-SSI  2 3/4" diameter compared to a CN-SS  2" diameter. That's the only difference. The difference in price represents the higher flow and higher capacities associated with the Imperial elements.