OK, I read through and it looks like things are in pretty good shape. So you got some bagged soil mix with pH that's lower than granny's nipples - welcome to the club. Many of us have fought it and it is absolutely not a death sentence for your grow. In the future, I recommend potting up some of your mix a few weeks before you germinate and doing some testing. If you find that it's low, that gives you a chance to mix in some dolomite lime and let it take effect. If it's high, you can add some iron/aluminum sulfate to get it neutralized. That way you are starting from a clean slate when the seed hits the soil, and you can mix and flush all you need to without affecting your plant. Water under the bridge at this point, so what to do now?
From what I can see, your soil is heavily ferted so I am skeptical that you need to be giving any food at all during the first weeks. Any yellowing is likely the result of overfeeding or pH lockout or both. I usually run at least to day 21 before feeding with heavily amended soils like that. As for testing and adjusting pH while growing organic - that is a personal preference thing. I usually do it with Earth Juice organic pH adjuster, though on my current grow I had a very active microherd and stopped bothering after a few weeks. My nutrient solution would be in the mid 5s and would drop the soil pH down to the low 6s, then as the days passed between watering the soil would drift back up to the mid to high 6s. It continued this buffering cycle throughout the grow and all I did was monitor with my Accurate 8 soil probe but didn't adjust anything. Keeping in mind that I had adjusted my soil to 6.5 prior to starting the grow. I use General Organics which seem to be similar to the Biobizz nutes and they say you only need to pH the water if you are using very low ppm tap water, distilled water, RO water, etc. Normal tap water with an EC of .3 or higher should have enough minerals to buffer the pH when added to an organic medium.
Like several others have said, I'd start by getting some kind of bottled water and pHing it to around 7-7.5 and flushing the soil until you see your runoff pH back near the normal range. Hopefully this will also help remove some of the organic matter in the soil so you can have better control over feeding. Before you do that, top dressing with dolomite lime would be a good idea so it can work down into the soil and start fixing this over the long term. While you're in lockout, some foliar treatment can be employed if you start to see signs of deficiencies. An organic seaweed mix is good, or even a synthetic food with lots of micronutes and a little N to green things up. Even though I grow organic, sometimes I use GH FloraMicro for foliar troubleshooting since it works fast and really stops any sort of spotting or yellowing almost instantly.
Once you're back in pH range you can resume some light feeding, and I would also recommend using some myco booster like Great White every couple of weeks just to make sure the little beasties are thriving. Anyway sorry to write a novel but trust me when I say I have battled through far worse and still harvested some nice plants, so don't let the temporary setbacks get you down. This is a marathon, not a sprint! :Sharing One:
