Assuming those numbers are accurate, looks like the root of the problem is your RO membrane. Did you let the system run for a few minutes before taking the tds measurements? I want to mae sure that you didn't measure tds creep water.

Also - What is your waste water to purified water ratio? Line up 8 identical cups in front of your system. With your waste water tube in one hand and your di tube in the other, in the time it takes you to fill 1 cup with di water, how many cups can you fill with waste water?

What is your water pressure?

Russ

Russ