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PharmHand
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Where’d you get the promix from? How old is it? There’s a manufacturer date stamp somewhere on the bails.... Peat is acidic by nature so lime is added to help neutralize ph. The lime is time released so if it’s been sitting awhile or maybe got damp it will activate the lime before the plants even get planted causing ph to be too low locking out your cal and mag causing issues and since your ph is soooo low very little of anything is being taken causing serious buildup. I grew in promix 20 gallon pots sealed rooms for 10+ years med to large scale and switched to coco for this very reason- always seemed to run into some sort of deficiency at some point.... It’s a great medium for learning or trying to manage large crops but it definitely has its weaknesses. I used to top dress w dolopril about 6 weeks after a plants been in the medium plus I’d add a little extra even at trans for same reason. A half cup per 20 at trans and a quarter cup top dress every 6 weeks. There’s a residual lime test you can do it explains it on the promix website