Thanks for the help.
I wrote to the company to ask about the TDS after the membrane being off and got this reply,
Hello Ben,
I wouldn't be terribly concerned. That after RO reading seems pretty on target, and out of the faucet your water is relatively clean (mine reads in the 300-400 range!). Depending upon the resolution of your TDS monitor, it could be something as simple as it reading a little higher than it actually is. I usually have a similar experience with my setup, and usually my readings start around 0-5 and once I have produced a decent amount it starts reading in the 10-15 range, but usually it isn't time for me to change cartridges until I see it read in the 20-30 range. Just let me know if you have any other questions!