I have been fighting a problem with my RODI for a year. I burn through RO membranes way too fast and the reason is unknown. I am lucky to get 400 gallons out of a new one and as they go south my DI resin is trying to compensate. For example I just changed the DI and after making 50 gallons it is 1/3 used. My incoming water is 210 ppm and afte the RO is is still 39 so you can see the problem. Just for reference I have researched this, talked to experts and even replaced the part that hold the membrane thinking it may be cracked all to no avail but I am still looking for suggestions. I religiously back wash the membrane and do not run hot water through it. Maybe I am just going to have to live with replacing the membrane every 7 months.