Water PPM on the Rise big time, even starting as low as 50 ppm.

hey guys question for you. I have 6 plants in an aero/nft system. they are roughly 4-6 inches tall. my tap water is 220ppm. I am adding only 50 ppm to my water, and yet after two days my ppm has doubled to 400. What should I be doing here to help ofset this drammatic increase. I'ts practically just tap water. I also use the hard water micro from GH. Should I be investing in a RO system? Is the increase in ppm because they are drinking more than they are eating? If so this would seem dramatic for my plants. Thanks guys.

I've never heard of the PPM rising like that, unless for some reason, there's a delay to the dissolving of your nutes. At any rate,...yes, I'd go with a RO system, 'cause any water over 150 PPM isn't recommended for growing.