Hi, how long do you find your membranes last? I have to change mine at least once, sometimes twice, a year. The manufacturers all seem to claim they last 3 -4 years! Mine are fine for a couple of months, single figure TDS, then it slowly but surely starts to creep up. I don't know if its something I'm doing wrong? My RO has 2 100GPD membranes, I change the filters regularly and flush it every day.