Typically, as nutes are taken up, pH will tend to rise. Emphasis on "typically" and "tend to".
For my last grow and for the last few weeks of the previous grow, pH would drop for a few days after every res change and then gradually start to rise, perhaps 0.1 units every few days. The last grow was Gorilla Glue, the grow before was Gelato, and both were autos.
What changed? I switched from Botanicare Kind to Jack's 3-2-1 (mixed 3.79-2.52-0 because there's a lot of Mn and S in the two nutes).
As a new grower, I followed the "Wonder Chart" document religiously and chased pH all the way down to EC 0.6. No bueno on that. These charts have been floating around for years; I've given them new names. They offer good general guidance and, being completely new at this (I just finished grow 4 - one in 2017 and three since 1/21), I "followed the directions" and ended up with my dick in my ear, speaking metaphorically, of course.
The pH drop could have been from not adding the Epsom salts - I don't understand nutes at the ion exchange - but, as a grower on another site explained to me, the drop in pH is simply a result of how the plant was taking up nutes and there was nothing to worry about. He certainly was right. Both grows did well, the last one yielding 729 gm from two autos in a 2' x 4'.
Like you, I considered getting a doser but I decided against it. One reason for that decision is that I think it's good to develop an understanding of what's going on in the grow environment rather than "paving over" issues with more chemicals. Having been through those grows, I'm glad that I didn't because it was a reproducible behavior and my preference is to change my nute mix to get a res that's 100% stable without intervention.*
Hope that makes sense.
*Writng this posting reminded me that Bugbee did a paper on managing nute solutions in recirculating systems and he listed the chemicals that are taken up very quickly.
View attachment 5186972View attachment 5186973 I'm thinking one of those is what's dropping my pH.
