Can do a slurry test to check PH or just check runoff. Bit in organics you dont really want runoff as you will be removing available nutrients from the soil in doing so.
Purple on the petiole only is likely light intensity to the exposed petiole. Are they green a bit lower or in the shaded area? If so thats the cause and its of no concern.
I find root temls of 70-80f to be very good especially 75-80f. Its not like hydro where we want lower root temps. Around 75-80f the microbes will thrive and it will speed up the metabolism of both the microbes and the plants.
Room tempa of 80-84f and matching that to the low end of VPD for indica leaders and high end for sativa leaners.
When having issues the best thing you can do is reduce the light intensity until fixed. With high transpiration rates you get more nutrients to the plants and its a common cause of calcium issues if its low due root, air temps or high humidity. Can also be affected by salinity from over feeding.
IMO stop the molasses and other crap feed some cal mag, reduce the light a bit, adjust the environment and make sure your keeping it between 30-60% saturated. Microbes don't like to be dried out and plants and microbes need o2 so in soil you don't want to fully saturate the soil when using organics as the microbes also use o2 and there will be a high population with organics because of the increased food source.
Do you think watering 1 gallon / 4.25 litres per 7 gallon pots is enough water to not saturate but not leave dry spots too ?