I try to use the least amount of bac water I can, like who wants to inject their rat with 50 plus units, I used 1.5 ML bac in a 500mg bottle and it 15 units for 75ml use the peptide critic calculator!
I have also had this same problem when I got some grey market nad in 10ml bottles, after looking at it I added 1ml more of bac and it dissolved the crystals. I figured i had noting else to lose. the next vial I used 1.5ml of bac and that seemed to be enough with no problems. you could always use 1.5ml in a new vial, and then add it to the problem vial instead of adding more to keep the volume low and the concentration higher.