Do you regularly get a ~20% runoff? if so, should be fine or at least can merely adjust formula slightly to fix what you see... if much less runoff each time, may need to dilute substrate a bit with a flush or possibly just reduce fertilization a bit -- frequency or concentration.
That could be lockout too. Use a web ppm calculator to help eliminate possibilities.. i don't know if my spreadsheet works for liquid nutes, but you could try that too. it is linked in my main GD profile in the comments section. Regardless, make sure it accounts for specific gravity if your lables are listed in w/v values. (or is it w/w? lol the instructions in spreadsheet mention this.. w/v makes more sense since the volumes mass changes with what is dissolved in it.) otherwise, it'll be off by large proportions
can't give a specific answer to this as too many variables ar eneeded... consider recent behaviour, do a little math... apply some deductive reasoning and go with the best possible course of action. pH is another thing to check before any drastic measures are taken... try to take a conservative path, if possible. easy to add something later, tougher to take it out, if wrong.