Hello I'm experiencing some phosphorus def and was thinking of upping big bud from 1ml to 2ml per litre. Not sure if it would be a bad move or not?
What age are your girls
At that age they are probably well into flower. I would be inclined to give them a quick flush and just feed as normal at about half the manufacturers recommended dose. A good flush can work wonders especially if the def is due to a lockout .
2 mL/Liter is the Advanced Nutrients' recommended dose. At 1 mL, you are only giving 1/2 dose. I don't think you can go wrong giving the amount that likely everybody else (including myself) uses and is recommended.