If your talking about watching the DVD's with he is just saying it is a simple system. Fill reservoir, add nutrients, check PH, check ppm and adjust accordingly.

In the DVD he does mention that the reservoir was never changed in the first grown and changed only once in the second and third grow.

I don't change the reservoir water in DWC systems either. IMO if the ppm and ph are right, there is no need to change the water.

Regarding the aquamist systems, has anyone ever built a DIY aquamist system? I mean it's just one big reservoir with a sprinkler head that mists all the roots underneath the cover. I've looked and looked for some kind of sprinkler or mister that could run off a water pump but I couldn't find any.