No pics, all thoughts...most of it pretty deep in the weeds. But if you use ProMix or another peat-based substrate, it's worth reading. I also want to tag in
@MrSauga,
@farside05, and
@FelipeBlu to make sure they stop by.
Many of you know
My tale of woe
That begins to show
When the leaves yel
-low.
Okay, enough of that. I want to talk about the issue I have of the rising pH of my ProMix HP that seems to affect my grows as I get into flower. My switch from Dr Earth soil to ProMix happened about the same time I went from FF trio to MC (early in 2018). And looking back on it this is where I probably began having a pH that was out of range by the end of flower. No matter what I did I would be losing lower leaves and seeing deficiencies I shouldn't have been having.
Some of that might be related to some of the odd ratios that MC v2 used (high Ca and K), but I have to think that the pH of the ProMix played a role as well. I didn't start checking substrate pH until later on in my growing.
[I hope you've read the first post in my thread about not having to pH our nutrient solutions in a buffered medium because I don't want to re-cover that ground here. If you haven't read it and you're interested, just read
the opening post here. We'll wait for you...]
So what is it about MC that doesn't seem to play well with ProMix, as I am not the only one to have had this issue. I've helped out other growers here correct their pH after a slurry test would show it was too high. So I decided to have a conversation about it with my contact at Premier Tech Horticulture, the manufacturer or ProMix.
I asked him why the pH of my medium seems to move out of range so quickly, where people using MC in soil don't seem to have that problem. This was his reply:
[Note: when he says "growing media" he's referring to peat-based like ProMix. Also, edited for clarity.]
"For...soil, the buffer and CEC is much greater than formulated growing media, therefore swings in pH and nutrition are less. Since...soil is highly buffered (depending on its source), it is also more resistance to change. That said, growing media allows growers to manipulate nutrition and pH for plants needs much easier. Managing the fertilizer with the alkalinity of your water is the key to achieving the ideal pH."
This means that soil is less sensitive to both the nitrogen source in the fertilizer (nitrate or ammoniacal), as well as the alkaline content of the water used. But the advantage to "growing media" is that it "allows growers to manipulate nutrition and pH for plants needs much easier." It will respond more quickly to changes you make in response to the plant's needs.
And his recommendation was to use two different types of nutrients in a rotation: two waterings with one higher in ammoniacal nitrogen (like the GrowMore Orchid stuff I use to bring down pH when it gets too high), followed by one watering with a fertilizer high in nitrate nitrogen, like MC. And to continue to monitor slurry pH to make sure it's staying in the correct range (5.5-6.2). He didn't think there was a single blend of the two N types that would work at all strengths.
Now, why would this affect me more than a lot of other growers using MC and "growing media"? Because, as farside mentioned, he and many tent growers are usually harvested by the time the plants are 120 days above ground. In that amount of time (with transplants into new media), the pH hasn't risen far enough to really matter to the plant's health. But mine are just starting flower about then, which is when I start to see the problems crop up.
So...move to a quality soil (like FFHF or Miracle Gro Natures Care Organic Potting Mix) and stick with MC, or move to the alternating system he recommended with ProMix? Farside is thinking that there might be a way to find a blend using MC and ammonium sulfate to keep the pH in check through flower. That blend will allow me to use the ammonium sulfate to add ammoniacal nitrogen (and a sulfur boost like Terpinator without the potassium) to keep the pH in check.
I am going to give that a test with the Jack Herer (now 69 days above soil), so that information will be part of those updates.
If you made it all the way down here,
for reading this!
to my perpetual grow journal! I did link the word "salve" in the post but sometimes that's hard to see on a phone. 
