Why different membranes? Can you just not adjust the back pressure to compensate for salinity? That's how I ran my homemade water maker. When I built the system my knowledge of ro was limited and bought membranes recommended by manufacturer. I use separate housing for cleaning and pickling and then store them away. Membranes seem to last years for me so I never changed my setup as new information came to me. I get good tests and I'm happy with the water taste and the amount of time I have to run to make water. I guess I'm running on if it's not broke don't fix it.