Hey DGC fam!
This saved my ass on the first autoflower I ever grew, and because calcium deficiency seems to be prevalent, here is an easy home made calcium foliar spray.
Cook eggshells in oven until dark brown (it will stink…). After cooled break them up as much as possible and put in a mason jar. Fill mason jar with vinegar and let it soak for a few days. It will activate when you put in the vinegar and start bubbling. When ready to use, dilute 1-2 teaspoons of calcium vinegar to a quart of water, add some transport for good measure and spray! The vinegar flashes off so the smell won’t be too bad for long and won’t hurt the plants. It’s also good for PM!
The plant I mentioned that this saved was just about beyond saving. It lost almost all of its fan leaves to a calcium deficiency 4 weeks into flower. This girl was in my second ever grow and was my biggest issue so far, I had no idea what to do and by the time I figured out how to address the issues it was real bad.. She was never super happy again, but after a few sprays and some nutrient management she started to come back strong and in the end, even without fan leaves, gave me 36 grams of dank ass bud off the stem! I call that a win! I hope this helps at least one person avoid the cal deficiency struggle.