Rockwell cubes to DWC setup

Can rockwell cubes be put directly into a DWC setup and then the roots grow out from there?

And what should i keep my ppm at?

Yes, they can.

thank you for you insightful reply

Yes, just put the cube at the bottom of a net pot and cover the base of the stem with some hydroton to block light and to support the stem. The roots will find their way into the water just keep it misted untill then, keep the water level right at the bottom of the pot. I go straight water or a light nute solution, think ~200ppm for the first 3 weeks or so, gradually increasing untill you're up to 1200-1600. Depends how safe you want to play it and how much the strain can take. Good luck.