Mr E, I switched my plants over to bloom about 2 weeks ago and finally noticed (several grows in) that the ph level in blooming nutes lean very strongly downward. I had been having the same issue you had recently...was using baking soda to keep it up but it would drop overnight which it NEVER did with the grow nutes. Guess I have been paying more attention since my molasses party. I'm now almost 3 weeks in 12/12 and am noticing the plants are now big enough to start shift the ph back upward. I'm convinced it's something in the difference between the grow and bloom nutes.