Yellow foam in 3 week veg DWC...HELP!

Ok, so I have been doing rez changes every other day on three of my DWC buckets for the last week. The day after rez change, I notice a bit of yellow foam ring around the waters edge in the bucket. The Ph also keeps rising. I Ph to 5.8 every morning, by evening, it's back at 6.5, and they are not eating, the ppms either stay the same or go up a bit. Yesterday, I noticed on two of the plants, they have a little brown on the roots, wipes right off with my fingers though. Any thoughts people?
3 gal DWC
Fox Farm nutes
Ppm range - 200-300 (depending on plant)
Supplements - AquaShield and Cal mag, 1 drop in each bucket of Superthrive
Room temp - 73-77
Rez temps - 64-69

There is no signs of anything wrong from looking at them.

Ok, so here is what a few of my buckets look like about the third to fourth day after rez change. The only thing these buckets have in common that the others don't is that they get Fox Farm Big Bloom. Now, my White Widow which is in week 3 of flowering had this issue a few times during veg and I thought it was root rot. But once I moved her into flowering, I was told by my hydro guy to feed her the Big Bloom, so I did. She is not getting the foam anymore. I wonder if it's because she is sucking up the nutes super fast and my veg plants are not. Any ideas?


The plants are not giving off any signs that something is wrong, other than the rising Ph and the ppm s don't adjust.