If its a new unit let 5 gallons or so flush through just to break it in. It should be good. If you need to test TDS just pick up a cheap one. I can help if you need. I'm in Riverside but I'm not home today.
I have this on my RO/DI and I like it. I can check tds going into my unit and tds coming out of it. I would recommend this that way you will know when your membrane starts to go bad also.