I just changed the resevoir again and cleaned the whole system with a a little bleach. I still don't know what the problem is but there seemed to be a bit of algae or maybe just some sediment on the bottom of the reservoir like I would find at the end of a 7 day reservoir.
What I am going to do since this has never happened to me before (quick pH drop and cloudy rez) is to eliminate a few things that I am trying differently. My last grow I didn't use Cal-Mag or Silica Blast until mid-flowering, and even then I'm not sure if it did anything. I use RO water so it sounded like something I needed by advice from other growers.