I miss the old 3 part formulation. The local hydro stores only carry the new gorilla line.
AN is okay, agree it’s not good value for money though.
I use big bud throughout flower no issues.
To OP are you in an organic soil? Or a inert medium like promix?
I’ve never used in organic, but in promix I use at around 75% of listed strength in flower and just gauge it. Start at water, nutes, water, nutes and adjust from there. If they are hungry I go longer between water only.
If you are watering with a good amount of run off say 15% or so of what you water with you shouldn’t have any toxic level build up, especially with water only every other or every few waterings.