Do not use DI if you have a 100 GPD Dow Filmtec NF or nano filter membrane. It IS NOT a Reverse Osmosis or RO membrane rated at 96-98% rejection rate and NSF/ANSI rated for drinking water but is a 90% rejection rate NF filter designed and rated by ANSI/NSF for "Pool and Spa Use". Huge difference and it will go through DI resin many times faster than a Dow Filmtec 75 GPD RO membrane which IS 96-98% rejection rate.

Any legitimate RO vendor will try their best to talk you out of the Dow 100. The reason is, for every 2% you decrease the rejection rate you cut your DI life in half, imagine what going from 90% to 96-98% or higher will do for your DI life and treated water quality. A huge cost savings.