You should get a handheld TDS
meter and measure your output water.
You shouldn't have a problem upping the output of the unit, provided the RO
chamber will hold a larger membrane, you would do better to address this to one of RO
selling sponsors in their forum, they should be able to guide you as to what is safe to upgrade to. Personally I would go with about a 75 gpd unit. As for the DI
, pretty much any DI
cartridge will do, if you have a TSDS meter, if not, make sure you get one with a color changing resin so you know when to change it