I sanitize mine once a month. I grow hydro and I try to leave them empty the night before a rez refill I turn on the RO machine. I used to let them sit around full they would get funky. You can always add some bleach in small doses. .25 ml per gallon, should dissapate in a day or so with...
I run the dyna-gro line.. once the PH is set it never moves for two weeks.. late in flower i might get a cal mg def so i bump the pH up to 6.2 and it let it fall back to 5.8 over three days. I do that twice. My plants look amazing.. If UC is the autopilot system then dyna gro is the auto...
I ran something like this, without the fogger. Pain to build and leak proof. K.I.S.S. pulled out the misters and added a simple drip ring, life is much better.
http://urbangardenmagazine.com/2010/07/extreme-aeroponics/