Well, I have not done this much pH testing since I worked in a water quality lab in the late seventies! Anyways, I found that it is normal for a pH rise when feeding due to ionic exchange and this actually signals a healthy uptake of nutes. However, I could not find any reason why there was a pH rise of a mixed nute solution prior to feeding. So the focus was to see if a stable pH could be maintained with the mixed nute solution that I'm using.
My original veg nutes were Canna Coco A&B (base nutes), Rhizotonic, Cannazym and General Organics CaMg. After approximately 24 hrs the pH would rise from about 5.5 (set points were all from 5.5-5.6) to 6.8 or so. My last grow in straight coco went well with the base nutes at around 3/4 of the Canna feed chart so I continued that. I wanted to see if I could isolate the pH rise to just the base nutes so I mixed the A&B and after a couple of hours would see the pH creep up and ended at around 6.2 after 24 hours so it seemed like this might work if I used the base nutes only and no supplements. I don't know what would have happened after 24 hrs.
I remembered all of the hype regarding Advanced Nutrients and their 'pH Perfect' technology when I was researching nutes a while ago, but did not really buy into it. But I was getting desperate and thought that it was worth the investment in their base grow nutes so I picked up the Sensi Grow A&B. I'll also give AN some bonus points because they responded to my email in a couple of hours which is good on its own...but I emailed them on Labor Day.
I started with a 50% dose of the AN base nutes and a couple of hours later the pH again was creeping up and after about 24 hours the pH was a little better than the Canna base nute solution, but not by much. So I said eff it, and hoped that if I increased the dosage (3/4) there would maybe be a stronger buffering effect and then added the supplemental nutes at a slightly lower dose. I started at 5.6 and after about 6 hours there was no pH rise so I crossed my fingers and checked the pH this morning (post 24 hrs). The pH rose to between 5.7 and 5.8 (meter fluctuated) so at this point there seems to be some hope. So this is where I'll be picking up and if it works out I'll probably get some more of the AN nutes. I can't say that the AN nutes are 'pH Perfect' but they may be 'pH Pretty Good'.
In the mean time, the plants were given a light flush yesterday until the effluent pH was down to around 6.2. I was running short on time when I did that, otherwise I would have dumped more pHed water through them.
The plants have been looking a little better lately, particularly the new growth, most likely due to the daily dumping of the Hempy reservoirs and the replenishment of a better pH solution. So right now I'm just going to let them drink the plain, pHed water for a couple of days before they resume getting any more nutes.