As far as getting acidic soil in flower, this is usually because peat based soils(pro-mix) have the potential for acidic build up from microbial leaching.
I've read organic nutes tend to be more acidic. And, I've read about peat's acidic tendency. Now you mention microbial leaching (don't know what that is), but it sounds like an interaction I wouldn't have if using non-peat soil, or a less organic nutrient? That adds a dimension to why my ph was more stable when using GH Flora Series (3 part). I thought it was GH Flora's ph buffering (for hydro, which could have helped). But, it's more that GH Flora didn't have (or feed) microbes?
pH your waterings to around 6.2-6.6 and you will probably drop your chances of this happening.
As the soil acidifies, say 6 weeks into the grow, I've been watering 6.8-7.2 which holds the soil ph higher. But, I don't like using the quantity of ph up. Sometimes I mix 1/8 tsp hydrated lime into the feed. Sometimes I use more Silica Blast (reluctant to use it in flower because silica isn't good for the lungs and I'm concerned using silica during flower might increase its presence in the buds). Therefore, I've been considering increasing dolomite levels, or using a small amount of hydrated lime to raise the initial ph of the soil.
But, I noticed something interesting. I have a plant that's mid- to late-flower and has had acidic soil. Last time watered I used water-only (just some 3ml/gal each Liquid Karma & Alaska Kelp, 1/2 tsp/gal Epsom salt, and 1tsp/gal my dissolved eggshell). I didn't even ph the water. It was just 6.6 in the end.
I fed that plant today at ph 6.8 and the runoff was
much higher than I expected. Like, 6.8.
I've already considered that I should alternate feed/water. Now I feel I should try this before going crazy with dolomite or hydrated lime in the initial soil.
I'm worried alternating water/feed is like reducing the strength of the nutrients and will reduce yield. Using GH Flora Series, I had it just at the nute-burn level and it performed well. I thought I was shooting for the same threshold (watching burned tips, backing off a little). Maybe organics are different.
Now I wonder if feeding half the nutrients with each watering would be better than alternating feed-water-feed.
(Sorry if hijacking OP's thread.).