What is this and why is it happening?

I think you're WAY overfeeding her... definite nute burn... and I don't see any PH record in your diary which might ALSO be a problem. I use Fox Farm myself, and I only grow autos so hear me out... at the age your ladies are, you've got much too much GrowBig in your nute mixture.. I never exceed 1 tsp per gallon of Grow Big - autos just can't handle it. Big Bloom is not a problem although you might want to back off by 1 tsp with that as well - at least for now. If this were my grow, I would flush - hard... run 3 gallons of ph'd water (ph it to between 6.0 and 6.5) for every 1 gallon pot size... you're growing in a 3 gallon so run 9 gallons of ph'd water through each pot... then let her dry out completely before giving her anything else... When she's dry, you can give her a nute mix of 1/2 tsp GrowBig and 2 tsp Big Bloom per gallon. ALWAYS ph everything you give your ladies! I'm sure you're doing this but will say it anyway - follow the regimen of water/feed/water/feed ... some folks even feed once, water twice, feed again, water twice again... etc. When you give it PLAIN water, give her enough so you're getting about 10-20% runoff... this ensures that the soil is getting cleaned out of any residual nutes or a build-up of salts.... If you don't have a PH pen to measure liquid, get one.... it's the single most important tool growers can have for a successful harvest - avoids a TON of problems throughout the grow. Ok... I've rambled on and on... I hope this helps! Good luck....