3 months later...
The drought was broken in September. It turned out to be the wettest September on record here. It was followed by the wettest October on record here. Way too wet for tomato plants - I should have planted rice
This week, we had days of temperatures in the low 20s and 30s. Today has finally warmed up into the 60s, I'm cleaning out the few remaining plants that froze hard. The mix in the buckets is still very cold. I just checked the mix temperature with a meat thermometer and it quickly dropped to 40F. I wish I had thought of checking the pro mix temperature when the air temperature was in the 20s.
With all of the rain in September and October - there's no way to know if RKN/FW3 could have splashed up into the buckets. I'm thinking that the pro mix temperature going below freezing is a good thing? Even during last year's very warm winter - there were two 3-day stretches of continuous freezing temperatures.
I didn't drill holes in 4 buckets and the mix is soaking wet. I will be drilling holes in them.