I just installed IntelliChlor SWCG yesterday, using the IC40 cell for my IG ~18K-20K pool. I'll finally know the gallon size when I refill it this time.

Price wise there isn't all that much difference between the IC20 & IC40 cells, so I went with the larger cell. I figured I could run it at a lower power setting than the IC20. It may or may not help with cell life also, running at the lower power setting.

I haven't run it yet, as I'm still working on remodeling and upgrading the pool equipment. I'm about 85-90% done with the remodeling, and hope to be filling the pool before this next weekend.