The 7th stage in the first one is a waste. It has a
GAC ffilter after the
DI. You can't get better than
DI so what is the
GAC doing at that point.
Also, the 100gph membrane is usually only rated at 90% rejections vs. 99% for the 75gpd or the 150gpd membrane (at least for the Filmtec ones that I've seen).
AirWaterIce does not reccomend using a
DI with the 100gpd because of the lower rejection rate. I ran mine that way for 3 years before switchng to the 150gpd membrane.