It will go up slightly at this time of year, you could try using a booster, I flush mine for about 10mins before making pure
and for a few minutes after Iv finished, I honestly don't know if flushing makes a difference as there are guys on here who say they
don't do it and get no problems with their membranes.
My water isn't metered so I will continue to flush. (4040 membrane ) some RO aren't designed to flush.