We do a steady flow of business re working these systems once folks understand just what the bought. This is a little confusing because of some conflicting jargon used above, but best as I can understand:

You have three vertical housings, which contain, in order of water flow: 5 mic sediment filter, `1 micron carbon block, 5 micron carbon block. Then a 100 gpd knock off brand 1oo gpd membrane, then a horizontal DI housing, then a in-line taste and odor (GAC) cartridge.

Your tap water has a tds of 154, your RO lowers that to 38, and your DI lowers that to 22. For sake of discussion let's assume these readings are accurate.

Let's talk about the configuration of the system, and then how your particular system is working.

In general, you want to protect the carbon blocks with your sediment filters. So the final sediment filter (you only have 1) should have a pore size smaller than or about equal to the pore size in the subsequent carbon block. You have a 5 mic sediment filter followed by a 1 micron carbon block. To maximize the performance of your system you'll want to go with a 1 micron sediment filter ahead of a 1 micron carbon block(s), OR go with a 5 micron sediment followed by a 5 micron block(s). Bottom line - use your carbon blocks to adsorb VOC's, not act primarily as sediment filters.

Next, you have a 100 gpd membrane. Unless you can determine the brand name, no telling what to expect from it.

Next you have a relatively small, horizontal DI housing. Horizontal housings for DI resin are a fundamental design flaw. For a short-term fix remove the DI housing from its current position and mount it in a vertical position with the water frlowing from the bottom up. For a better solution get a full size, vertical DI housing with a refillabel cartridge.

Now, assuming your DI resin was operating as it should, you then take water that is as clean as you can make it and run it through GAC. Another fundamental design flaw. Remove the final horizontal in-line GAC cartridge. It is not needed and is counterproductive in the current configuration of your system.

Now, on to the performance of your system:
Your membrane is rejection only about 75 % of the tds in the feed water. Assuming you have adequate pressure, you can do 90%+ with a 100 gpd Filmtec membrane; and 96to 98%+ with a 75 gpd or 50 gpd Filmtec membrane. I recommend you replace the membrane.

You are getting 22 ppm tds water after it comes out of the DI and has passed through the GAC. First, as mentioned above, get rid of the post DI GAC. Run the system again for a few minutes and get a post-DI reading again. It may be near 0. Remember that the post DI GAC will ADD dissolved solids.

Russ @ BFS