HELP!!! I keep killing RO Membrane's

[chrisguy]

Background my tap water is about 120-130ppm. I flush the membrane every 2-3 weeks for about 1-2 minutes.

I bought my RO unit a little over a year ago. It's a 4 stage unit and was originally 50 gpd. After the first 6 months I replaced the sediment, carbon and DI. Shortly after that I found that I very quickly went through a DI cartridge, in about 1 month. In testing my water, the RO rejection had jumped from 2 - 4 ppm to about 25 - 30ppm.

So, under advice, I replaced the membrane with a 75 gpd and the flow restrictor. I could once again see a RO production water at 1-2ppm.

Low and behold a couple months ago I replaced the sediment, carbon and DI again and once again the RO rejection rate went up. This time I've tried to troubleshoot the issue to no avail. I did notice that the water pressure had dropped since the water company installed some a meter (was a little over 40psi before, dropped to a little over 30), so I purchased a booster pump. This added pressure, but I was still slowly eating DI cartridges. The RO production was back in the 20ppm range. The booster pump was installed post sediment and post carbon. I found conflicting information on if it should be pre or post carbon. Since the sediment and carbon were connected, I installed it post.

Tonight I removed the membrane to look for trouble, not that I knew what I was looking for. After putting it back in and flushing the membrane, the post RO membrane water is now 60 - 70ppm.

I did test the TDS meter and it is changing values and the in and out will read the same values when located pre or post DI.

I realize the RO membrane is once again bad and have ordered (again) a new one, this time a 100gpd with flow restrictor.

Can someone please tell me what the heck am I doing wrong?? I cant afford to replace EVERYTHING every 6 months.

Thanks in advance!!!!