Nutrient lockout

I would like to know what to do if you are experiencing nutrient lockout.I'm pretty sure that's my problem .The plants have been budding for about one month.I'm growing in Pro-Mix BX.

Flush thoroughly and fix your pH. For soil aim for roughly 7. If you have the ability to do it more precise, try to run a little lower. Then, you can check for deficiencies and add accordingly.

i am using promix hp and i have had nothing but problems with my ph since. there is a ph buffer in it and i cannot get my ph right. grow after grow i have had lockout issues due to ph everytime and just couldn't figure out why it would take many hours and gallons of flushing before the ph finally would get to where i want it. and that only happened because i think the ph buffer gets washed out. can't seem to find anyone with the same problem. by the way i have a very nice ph meter that's always cleaned and calibrated and i always monitor and adjust ph.