usually the lower output membranes have a higher rejection rate.
many "complaints" about the low cost "ebay"
RO/DI filters is that they use cheap
RO membranes. the fact is the 100 GPD membranes do have lower rejection rates, but aren't really less in quality.
besides if your output is 0 how much better can you get..
that said, if you have a 100 GPD membrane and you need better rejection you can try a 75 GPD to get better output..
